drm/amd/pm: update the data type for retrieving enabled ppfeatures

Use uint64_t instead of an array of uint32_t. This can avoid
some non-necessary intermediate uint32_t -> uint64_t conversions.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>