Add a missing bcopy() to make saving the VESA state actually work.

Add a missing bcopy() to make saving the VESA state actually work.
Also save the DAC state, increase the maximum save state size from
4k to 8k, and refuse to save the VESA state if the BIOS reports it
is larger than the maximum size we can handle.

It doesn't appear that anything currently uses this code, but it
turns out to be capable of restoring some notebook displays to a
working state after a suspend-resume cycle.