drm/amdgpu: clear ras controller status registers when interrupt occurs

To fix issue that ras controller interrupt cannot be triggered anymore after
one time nbif uncorrectable error. And error count is stored in nbif ras object
for query.

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>