drm/amdgpu: add yellow_carp_reg_base_init function for yellow carp (v2)

This patch adds yellow_carp_reg_base_init function to init the register
base for yellow carp.

v2: squash in updates (Alex)

Signed-off-by: Aaron Liu <aaron.liu@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>