drm/amd/pp: Add edit/commit/show OD clock/voltage support in sysfs

when cat pp_od_clk_voltage it show
OD_SCLK:
0:        300Mhz        800 mV
1:        466Mhz        818 mV
2:        751Mhz        824 mV
3:       1019Mhz        987 mV
4:       1074Mhz       1037 mV
5:       1126Mhz       1087 mV
6:       1169Mhz       1137 mV
7:       1206Mhz       1150 mV
OD_MCLK:
0:        300Mhz        800 mV
1:       1650Mhz       1000 mV

echo "s/m level clock voltage" to change
sclk/mclk's  clock and voltage

echo "r" to restore default value.
echo "c" to commit the user setting.

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>