drm/amdgpu: Fix MPEG2, MPEG4 and VC1 video caps max size

1920x1088 is the maximum supported resolution.

Signed-off-by: David Rosca <david.rosca@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 1a0807fe)
Cc: stable@vger.kernel.org