drm/amdgpu: fix missing stuff in NBIO v7.11

add get_clockgating_state, update_medium_grain_light_sleep and
update_medium_grain_clock_gating in nbio_v7_11_funcs
v1:
add missing funcs in nbio_v7_11.c
v2:
modify the if condition and add spport for nbio v7.11 clockgating.

Signed-off-by: Li Ma <li.ma@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>