[Intel-gfx] BIOS fb wrapping

[Jesse Barnes]

I split these out for clarity and ease of review.  They seem to be
working ok here now, and correctly taking the previous fb and using it.

The memset patch makes plymouth look better on this machine (it doesn't
flicker black near the end).

I haven't tested this on as many configs as the old patchset (dual head,
misc grub configs, etc), so extra testing would also be welcome.

Thanks,
Jesse