scripts/gdb/symbols: factor out pagination_off()

Move the code that turns off pagination into a separate function.  It will
be useful later in order to prevent hangs when loading symbols for kernel
image in physical memory during s390 early boot.

Link: https://lkml.kernel.org/r/20250515155811.114392-3-iii@linux.ibm.com


Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>