drm/amdgpu: Introduce another ras enable function

Many parts of the whole SW stack can program the ras enablement state
during the boot. Now we handle that case by adding one function which
check the ras flags and choose different code path.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>