powerpc: Drop GPL boilerplate text with obsolete FSF address

The FSF does not reside in the Franklin street anymore, so we should not
request the people to write to this address. Fortunately, these header
files already contain a proper SPDX license identifier, so it should be
fine to simply drop all of this license boilerplate code here.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250711072553.198777-1-thuth@redhat.com