radeon/vcn: add H.264 constrained baseline support

VCN supports this profile as well as UVD, so add it

Signed-off-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
CC: <mesa-stable@lists.freedesktop.org>
(cherry picked from commit f8ef8b56)