drm/amdgpu: add fw load type flag for rlc autoload

Add another firmware load type AMDGPU_FW_LOAD_RLC_AUTO to support firmware
autoloading new feature in gfx10.

This flag can be leveraged for future engines that need autoload fw.

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