drm/amd/pm: Add get_gfx_off_status interface for yellow carp

add get_gfx_off_status interface to yellow_carp_ppt_funcs structure.

Signed-off-by: Shikai Guo <shikai.guo@amd.com>
Reviewed-by: Aaron Liu <aaron.liu@amd.com>
Reviewed-by: Prike Liang <prike.liang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>