drm/nouveau/bios: add opcodes 0x73 and 0x77

No known VBIOSes use these, but they are present in the actual VBIOS
table parsing logic. No harm in adding these too.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>