Description of problem: ReaR may fail to install GRUB and set boot order after restore due to missing `/dev/nvram` making the system unbootable.

Version-Release number of selected component (if applicable): rear-2.6-11.el9.ppc64le

How reproducible: always

Steps to Reproduce:
1. Create a rescue image (e.g. ISO) and backup using `rear mkrescue` on a ppc64le machine.
2. Boot into such rescue system.
3. Run `rear recover` and answer all questions with affirmative replies.

Actual results:
GRUB 2 fails to install due to missing `/dev/nvram` and the boot order will not be changed to the corresponding block device.

Expected results:
GRUB 2 installs successfully and the boot order is set to corresponding block device.

Additional info:
- On newer kernels, the NVRAM driver is built as a kernel module which needs to be loaded so that `/dev/nvram` is created.  ReaR must load this kernel module before installing GRUB 2 and  changing the boot order.

- logs:
>2022-05-18 01:36:01.321238142 Including finalize/Linux-ppc64le/660_install_grub2.sh
>/sbin/grub2-probe
>2022-05-18 01:36:01.322570843 Installing GRUB2 boot loader on PPC64/PPC64LE...
>Generating grub configuration file ...
>Adding boot menu entry for UEFI Firmware Settings ...
>done
>2022-05-18 01:36:11.099705611 Determining where to install GRUB2 (no GRUB2_INSTALL_DEVICES specified)
>2022-05-18 01:36:11.103006970 Found PPC PReP boot partition /dev/sda1 - installing GRUB2 there
>dd: writing to '/dev/sda1': No space left on device
>8193+0 records in
>8192+0 records out
>4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.0771412 s, 54.4 MB/s
>Installing for powerpc-ieee1275 platform.
>nvram: ERROR: cannot open "/dev/nvram": No such file or directory
>nvram: ERROR: cannot open "/dev/misc/nvram": No such file or directory
>grub2-install: error: `nvsetenv' failed. 
>You will have to set `boot-device' variable manually.  At the IEEE1275 prompt, type:
>  setenv boot-device /vdevice/v-scsi@30000003/disk@8100000000000000
>.
>2022-05-18 01:36:13.883630644 Failed to install GRUB2 on PPC PReP boot partition /dev/sda1
>2022-05-18 01:36:13.889924451 Failed to install GRUB2 - you may have to manually install it
>2022-05-18 01:36:13.893384398 Including finalize/Linux-ppc64le/680_install_PPC_bootlist.sh
>2022-05-18 01:36:13.903409037 PPC PReP Boot partition found: /dev/sda1
>2022-05-18 01:36:13.911498962 Boot device disk is /dev/sda.
>2022-05-18 01:36:13.919528935 Set LPAR bootlist to '/dev/sda'
>/usr/sbin/nvram: ERROR: cannot open "/dev/nvram": No such file or directory
>/usr/sbin/nvram: ERROR: cannot open "/dev/misc/nvram": No such file or directory
>Could not update bootlist!
>2022-05-18 01:36:14.280003500 Including finalize/default/880_check_for_mount_by_id.sh
>2022-05-18 01:36:14.289783287 Including finalize/default/890_finish_checks.sh
>2022-05-18 01:36:14.302983687 WARNING:
>For this system
>RedHatEnterpriseServer/9 on Linux-ppc64le (based on Fedora/9/ppc64le)
>there is no code to install a boot loader on the recovered system
>or the code that we have failed to install the boot loader correctly.
>Please contribute appropriate code to the Relax-and-Recover project,
>see http://relax-and-recover.org/development/
>Take a look at the scripts in /usr/share/rear/finalize - for example
>for PC architectures like x86 and x86_64 see the script
>/usr/share/rear/finalize/Linux-i386/660_install_grub2.sh
>and for POWER architectures like ppc64le see the script
>/usr/share/rear/finalize/Linux-ppc64le/660_install_grub2.sh
>---------------------------------------------------
>|  IF YOU DO NOT INSTALL A BOOT LOADER MANUALLY,  |
>|  THEN YOUR SYSTEM WILL NOT BE ABLE TO BOOT.     |
>---------------------------------------------------
>You can use 'chroot /mnt/local bash --login'
>to change into the recovered system and
>manually install a boot loader therein.

- upstream PR with a fix: https://github.com/rear/rear/pull/2580