drm/amdgpu: Move mmhub ras block init to ras sw_init

drm/amdgpu: Move mmhub ras block init to ras sw_init

Initialize mmhub ras block only when mmhub ip block
supports ras features. Driver queries ras capabilities
after early_init, ras block init needs to be moved to
sw_init.

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