drm/amdgpu: protect RAS sysfs during GPU reset

MMHub EDC becomes dirty after BACO reset

EDC registers should be cleared early on in reset phase

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>