drm/nouveau/bios: translate ramcfg strap through M0203

A machine has been spotted where the ramcfg strap is "8", and the ramcfg
xlat table goes 0-7,0-7, resulting in us selecting config 0 for memory
items.  On this particular system, config "8" is available and supposed
to be used.  It appears that starting from GT21x (where Mv2 appears),
we're supposed to use the value in this table instead.

One concern here is that not all the places we currently use ramcfg xlat
are supposed to be treated the same now.  The strap xlat table wasn't
removed from the vbios either, presumably for some kind of good reason.

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