drm/radeon/dpm: add infrastructure to properly handle bapm

bapm is a pm feature for sharing the power budget between
the GPU and the CPU on APUs.  It needs to be enabled or
disabled in certain circumstances.  For now, disable it
when on battery and enable it when on AC power.

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_pm.c
Simple merge