drm/nv40/pm: parse geometric delta clock from vbios

This changes the meaning of what we reported as "core" clock previously.

The shader/rop units are allegedly supposed to be run at the base clock
listed in the perf table, while the geometric clock can be bumped from
this value on some boards.

So that we can report both, we'll report the base clock as "shader" (since
the shaders *do* run at it), and the geometric clock as "core".

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