drm/amd/powerplay: optimization feature mask function for asic

1.change function return value type: from "unallowed" to "allowed"
2.replace feature mask number with feature macro, the code will clear.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>