drm/amdgpu: Add bounds checking to ib_{get,set}_value

drm/amdgpu: Add bounds checking to ib_{get,set}_value

The uvd/vce/vcn code accesses the IB at predefined offsets without
checking that the IB is large enough. Check the bounds here. The caller
is responsible for making sure it can handle arbitrary return values.

Also make the idx a uint32_t to prevent overflows causing the condition
to fail.

Signed-off-by: Benjamin Cheng <benjamin.cheng@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org