add support that allow the userspace tool like RGP to get the GFX clock
value at runtime, the fix follow the old way to show the min/current/max
clocks level for compatible consideration.

=== Test ===
$ cat /sys/class/drm/card0/device/pp_dpm_sclk
0: 200Mhz *
1: 1100Mhz
2: 1600Mhz

then run stress test on one APU system.
$ cat /sys/class/drm/card0/device/pp_dpm_sclk
0: 200Mhz
1: 1040Mhz *
2: 1600Mhz

The current GFXCLK value is updated at runtime.

BugLink: https://gitlab.freedesktop.org/mesa/mesa/-/issues/5260Reviewed-by: Huang Ray <Ray.Huang@amd.com>
Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>