Log if DPM is disabled

Currently, nothing is logged, if DPM is disabled.

$ dmesg | grep -i dpm
[    0.000000] Command line: BOOT_IMAGE=/boot/bzImage-5.4.39.mx64.334 root=LABEL=root ro crashkernel=256M console=ttyS1,115200n8 console=tty0 init=/bin/systemd audit=0 random.trust_cpu=on amdgpu.dpm=0
[    0.143948] Kernel command line: BOOT_IMAGE=/boot/bzImage-5.4.39.mx64.334 root=LABEL=root ro crashkernel=256M console=ttyS1,115200n8 console=tty0 init=/bin/systemd audit=0 random.trust_cpu=on amdgpu.dpm=0
[   15.073233] [drm] add ip block number 5 <si_dpm>
$ more /sys/module/amdgpu/parameters/dpm
0

A log message would be nice, to indicate, that the Linux command line parameter had an effect.