drm/amd/powerplay: Port vega10_hwmgr.c over to PP_CAP

Replace and cleanup lengthy phm_cap_enabled() sequences
with PP_CAP.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>