drm/radeon/kms: add atom helper functions for dpm (v3)

dpm needs access to atombios data and command tables
for setup and calculation of a number of parameters.

v2: endian fix
v3: fix mc reg table bug

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

diff --cc drivers/gpu/drm/radeon/radeon.h
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_atombios.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_mode.h
Simple merge