vpaes: LoongArch: Use getauxval(AT_HWCAP) for LSX detection

vpaes: LoongArch: Use getauxval(AT_HWCAP) for LSX detection

Running LSX instructions requires both the hardware support and the
kernel support.  The `cpucfg` instruction only tests the hardware
support, causing a SIGILL if the hardware supports LSX but the kernel
does not.

Use `getauxval(AT_HWCAP)` as the ["Software Development and Build
Convention for LoongArch Architectures"][1] manual suggests.

The LOONGARCH_HWCAP_LSX and LOONGARCH_HWCAP_LASX bits are copied from
the manual too.  In Glibc 2.38 they'll be provided by <sys/auxv.h> as
well, but they are unavailable in earlier Glibc versions so we cannot
rely on it.

The getauxval syscall and Glibc wrapper are available since day one
(Linux-5.19 and Glibc-2.36) for LoongArch.

Fixes #21508.

[1]:https://github.com/loongson/la-softdev-convention/blob/master/la-softdev-convention.adoc#kernel-constraints

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21509)