drm/amd/powerplay: add Fiji DPM support.

This enabled DPM support for Fiji.  DPM is dynamic
clock and voltage scaling.

v2: rename fiji_hwmgr_early_init to fiji_hwmgr_init
v3: (agd) fold in endian fix, additional function addition

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Eric Huang <JinHuiEric.Huang@amd.com>