Description of problem:
The PV framebuffer doesn't work on shadow translate mode, because it doesn't
translate gpfn to mfn.  Upstream doesn't need that translation, because the
hypervisor accepts gpfns in 3.0.4.

How reproducible:
always

Steps to Reproduce:
1. Make sure pvfb is enabled (it is by default)
2. Start the pv domain, e.g. with xm create DOMNAME
  
Actual results:
pvfb backend daemon dies during startup.

Expected results:
pvfb backend process runs.

Additional info:

var/log/xen/xend-debug.log:
/local/domain/0/backend/vfb/2/0 on fire (Invalid argument)
/local/domain/0/backend/vkbd/2/0 on fire (Invalid argument)