drm/amdgpu: add function to clear MMEA error status for aldebaran

For aldebaran, hardware will not clear error status automatically when
reading error status register, insteadly driver should set clear bit of
the error status register explicitly to clear error status.

Signed-off-by: Dennis Li <Dennis.Li@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>