drm/amdgpu: add helper to init rlc firmware

To initialzie rlc firmware according to rlc
firmware header version

v2: squash in backwards compat fix

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>