drm/amd/powerplay:add hwmgr callback to update nbpstate on Carrizo

Add hwmgr callback "update_nbdpm_pstate".This will use to access
"cz_nbdpm_pstate_enable_disable" function to enable/disable low
memory pstate.

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