drm/radeon/uvd: revert lower msg&fb buffer requirements on UVD3

This only seem to work for H.264 but not for VC-1 streams.

Need to investigate further why exactly.

This reverts commit 4b40e592.

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>