scripts/gdb: add 'lx-kasan_mem_to_shadow' command

This command allows users to quickly translate memory address to the kasan
shadow memory address.

Example output:
(gdb) lx-kasan_mem_to_shadow 0xffff000019acc008
shadow addr: 0xffff600003359801

Link: https://lkml.kernel.org/r/20240723064902.124154-6-kuan-ying.lee@canonical.com


Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>