drm/amdgpu: fix division by zero with invalid uvd dimensions

drm/amdgpu: fix division by zero with invalid uvd dimensions

When width or height is less than 16, width_in_mb or height_in_mb
becomes 0, leading to fs_in_mb being 0. This causes a division by
zero when calculating num_dpb_buffer in H264 and H264 Perf decode
paths.

Add validation to reject frames with width < 16 or height < 16
before performing any calculations that depend on these values.

V2: Format change - move up all vaiable definitions.
V3: Use warn_once to avoid spam.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 3e41d26c70b0a459d041cc19482a226c4b7423cb)
Cc: stable@vger.kernel.org