drm/amdgpu: add custom power policy support in sysfs

when cat pp_power_profile_mode on Vega10
NUM        MODE_NAME BUSY_SET_POINT FPS USE_RLC_BUSY MIN_ACTIVE_LEVEL
  0 3D_FULL_SCREEN :             70  60          1              3
  1   POWER_SAVING :             90  60          0              0
  2          VIDEO*:             70  60          0              0
  3             VR :             70  90          0              0
  4       COMPUTER :             30  60          0              6
  5         CUSTOM :              0   0          0              0

the result show all the profile mode we can support and custom mode.
user can echo the num(0-4) to pp_power_profile_mode to select the profile
mode or can echo "5 value value value value" to enter CUSTOM mode.
the four parameter is set_point/FPS/USER_RLC_BUSY/MIN_ACTIVE_LEVEL.

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