drm/nve0/fb/gddr5: parse bios data into struct rather than using directly

Still essentially a struct of magic values with magic names and unknown
purposes.  But, we will shortly need to be able to mix and match bits of
the previous and next configurations to do a transition reclock, as such,
we can no longer directly use the vbios data with any ease.

This is probably nicer anyway in the long run, for a few reasons.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>