drm/radeon/atom: add new voltage fetch function for hawaii

Some hawaii boards use a different method for fetching the
voltage information from the vbios.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

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

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