Comment # 10 on bug 1176757 from Stefan Dirsch

Sound good, but seems you didn't run 'mkinitrd' afterwards. Not sure why this
worked then. So could you please make me a favor and run
'mkinitrd' and then please verify if things are still working with new *and*
old kernel?

This is a bug in AMD's amdgpu driver packages and would need to be fixed by
AMD. Unfortunatley for now you need to do this workaround (at least copying the
firmware files to the new kernel firmware directory) for each kernel update.
:-(