Just like arm64, riscv, and x86 move extable related functions to
mm/extable.c. This is currently only one function, but this will
change with subsequent changes.
Reviewed-by: NAlexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: NHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>