FROMGIT: selinux: Move avtab_hash() to a shared location for future reuse

This is a preparation patch, no functional change.

Signed-off-by: Hongru Zhang <zhanghongru@xiaomi.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
(cherry picked from commit 929126ef4a0e2723622eb3ba11017ca5fecd37d3 https: //git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git)
Link: https://lore.kernel.org/all/a878f27f8148bb4cc662755f6e69400632183477.1761217900.git.zhanghongru@xiaomi.com/



Bug: 455778108
Change-Id: Ibf6acd28d6f47860fd022c1cb2fab9c6c59e6ffd
Signed-off-by: liliang <v-liliang6@xiaomi.corp-partner.google.com>