drm/amdgpu: support gfx ras error injection and err_cnt query

check gfx error count in both ras querry function and
ras interrupt handler.

gfx ras is still disabled by default due to known stability
issue found in gpu reset.

Signed-off-by: Dennis Li <Dennis.Li@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>