Description of problem:
Cannot create nor update VM, where the "Single PCI" check box is checked first and the console type is then switched to VNC.

Version-Release number of selected component (if applicable):
rhevm-3.3.0-0.22.master.el6ev.noarch (is15)

How reproducible:
100%

Steps to Reproduce:
1. Open `Create VM` or `Edit VM` dialog, set the mandatory VM name.
2. On `Console` tab, make sure the console type is set to SPICE and `Single PCI` is checked.
3. Then change console type to VNC and submit.

Actual results:
Cannot add/edit VM. Cannot set single display device via VNC display.

Expected results:
`Single PCI` shoud be automatically turned off when the console type is not SPICE. The VM should be created/updated successfully.

Additional info:

A good use case where this can happen is to try to create a VM with Linux-based OS (where Single PCI is enabled by default) and just switch console type to VNC.