nv50: fix some h264 interlaced decoding on vp2

Some videos specify mb_adaptive_frame_field_flag instead of
field_pic_flag. This implies that the pic height needs to be halved, and
this field needs to be passed to the VP engine.

Cc: "9.2" mesa-stable@lists.freedesktop.org

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
(cherry picked from commit 8edb79f1ef95581c20ed0c3dc49aabe99d7f072a)
nvc0: force use of correct firmware file

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
(cherry picked from commit e847b5ae066bf9a209dad482fcc664f944983633)