[Intel-gfx] [WIP] Wrap fb objects from BIOS/bootloader

[Jesse Barnes]

There was a TODO from last time that Daniel and I talked about:
  - reconstruct fb state in our get_config callbacks instead
  - reconstruct per-crtc fb state and allocate separate buffers if
    needed
  - make sure we only preserve the buffer if it's the preferred mode

Just wanted to get this refreshed version out there to get some eyes on
it.

Thanks,
Jesse