drm/nv4c/mc: nv4x igp's have a different msi rearm register

See https://bugs.freedesktop.org/show_bug.cgi?id=74492

Reported-by: Ronald <ronald645@gmail.com>
Suggested-by: Marcin Kościelnicki <koriakin@0x04.net>
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>