drm/amdgpu: Print kernel message when error logged by scrub

Print a kernel message when the scrub bit of status register is set to
indicate that errors are being logged by the scrub.

Signed-off-by: Xiang Liu <xiang.liu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>