drm/amdgpu: Add place holder for soc15 asic init on emulation

Add common smu_soc_asic_init function to emulate the sillicon post sequence

Signed-off-by: Shaoyun Liu <Shaoyun.Liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>