drm/amd/powerplay: add some sysfs interfaces for powerplay.

drm/amd/powerplay: add some sysfs interfaces for powerplay.

The new sysfs interfaces:
pp_num_states: Read-only, return the number of all pp states, 0 if powerplay is not available.
pp_cur_state: Read-only, return the index number of current pp state.
pp_force_state: Read-write, to write a power state index will switch to selected state forcedly and
		enable forced state mode, disable forced state mode. such as "echo >...".
pp_table: Read-write, binary output, to be used to read or write the dpm table, the maximum
		file size is 4KB of page size.
pp_dpm_sclk: Read-write, reading will return a dpm levels list, to write an index number will force
		powerplay to set the corresponding dpm level.
pp_dpm_mclk: same as sclk.
pp_dpm_pcie: same as sclk.

And add new setting "manual" to the existing interface power_dpm_force_performance_level.

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