drm/nouveau/acpi: allow non-optimus setups to load vbios from acpi

commit a3d0b1218d351c6e6f3cea36abe22236a08cb246 upstream.

There appear to be a crop of new hardware where the vbios is not
available from PROM/PRAMIN, but there is a valid _ROM method in ACPI.
The data read from PCIROM almost invariably contains invalid
instructions (still has the x86 opcodes), which makes this a low-risk
way to try to obtain a valid vbios image.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76475
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>