I installed it now, but still no luck.

glopes ~ $ ls -l /lib/firmware/radeon/PITCAIRN_mc*
-rw-r--r-- 1 root root 31100 Mai 13 18:58 /lib/firmware/radeon/PITCAIRN_mc2.bin
-rw-r--r-- 1 root root 31076 Mar 23 02:02 /lib/firmware/radeon/PITCAIRN_mc.bin

When I run with radeon.dpm=0, it seems to load the correct file:

[    0.630585] [drm] radeon: 4096M of VRAM memory ready
[    0.630586] [drm] radeon: 1024M of GTT memory ready.
[    0.630593] [drm] Loading PITCAIRN Microcode
[    0.630632] [drm] radeon/PITCAIRN_mc2.bin: 31100 bytes
[    0.630644] [drm] Internal thermal controller with fan control
[    0.630673] [drm] radeon: power management initialized

I'm attaching the full log as well.