don't use asm accelerated path on big endian power9

don't use asm accelerated path on big endian power9

https://github.com/openssl/openssl/issues/29845

Found that our hardware accelerated path doesn't work on big endian
systems, so make sure that we only use it when little endian is defined

We also noted that PPC_AES_GCM_CAPABLE gets defined to zero when the
capabilities register notes that the hardware isn't capable of the
needed instructions, but that still includes the asm path as
PPC_AES_GCM_CAPABLE is still defined.

Fix both issues

Fixes #29845

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
MergeDate: Tue Feb 17 14:11:46 2026
(Merged from https://github.com/openssl/openssl/pull/29968)