drm/amd/pp: Print out voltage/clock range in sysfs

when user cat pp_od_clk_voltage
add display info about the sclk/mclk/vddc range that user can overdrive
output as:
OD_SCLK:
0:        300MHz        900mV
1:        400MHz        912mV
2:        500MHz        925mV
3:        600MHz        937mV
4:        700MHz        950mV
5:        800MHz        975mV
6:        900MHz        987mV
7:       1000MHz       1000mV
OD_MCLK:
0:        300MHz        900mV
1:       1500MHz        912mV
OD_RANGE:
SCLK:     300MHz       1200MHz
MCLK:     300MHz       1500MHz
VDDC:     700mV        1200mV

also
1. remove unnecessary whitespace before a quoted newline
2. change unit of frequency Mhz to MHz

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>