media: hantro: Reduce H264 extra space for motion vectors

A decoded 8-bit 4:2:0 frame need memory for up to 448 bytes per
macroblock with additional 32 bytes on multi-core variants.

Memory layout is as follow:

+---------------------------+
| Y-plane   256 bytes x MBs |
+---------------------------+
| UV-plane  128 bytes x MBs |
+---------------------------+
| MV buffer  64 bytes x MBs |
+---------------------------+
| MC sync          32 bytes |
+---------------------------+

Reduce the extra space allocated now that motion vector buffer offset no
longer is based on the extra space.

Only allocate extra space for 64 bytes x MBs of motion vector buffer
and 32 bytes for multi-core sync.

Fixes: a9471e25 ("media: hantro: Add core bits to support H264 decoding")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>