drm/amd/pm: add the fine grain tuning function for vangogh

This patch is to add the fine grain tuning function for vangogh.
This function uses the pp_od_clk_voltage sysfs file to configure the min
and max value of gfx clock frequency or restore the default value.

Command guide:
echo "s level value" > pp_od_clk_voltage
        "s" - set the sclk frequency
        "level" - 0 or 1, "0" represents the min value,  "1" represents
        the max value
        "value" - the target value of sclk frequency, it should be
        limited in the safe range
echo "r" > pp_od_clk_voltage
	"r" - reset the sclk frequency, restore the default value
        instantly
echo "c" > pp_od_clk_voltage
        "c" - commit the min and max value of sclk frequency to the system
        only after the commit command, the setting target values by "s" command
        will take effect.
Example:
1)check the default sclk frequency
	$ cat pp_od_clk_voltage
	OD_SCLK:
	0:        200Mhz
	1:       1400Mhz
	OD_RANGE:
	SCLK:     200MHz       1400MHz
2)use "s" -- set command to configure the min or max sclk frequency
	$ echo "s 0 600" > pp_od_clk_voltage
	$ echo "s 1 1000" > pp_od_clk_voltage
	$ echo "c" > pp_od_clk_voltage
        $ cat pp_od_clk_voltage
	OD_SCLK:
	0:        600Mhz
	1:       1000Mhz
	OD_RANGE:
	SCLK:     200MHz       1400MHz
3)use "r" -- reset command to restore the min and max sclk frequency
	$ echo "r" > pp_od_clk_voltage
        $ cat pp_od_clk_voltage
	OD_SCLK:
	0:        200Mhz
	1:       1400Mhz
	OD_RANGE:
	SCLK:     200MHz       1400MHz

Signed-off-by: Xiaojian Du <Xiaojian.Du@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>