ec: powerpc64le: Add asm implementation of felem_{square,mul}

ec: powerpc64le: Add asm implementation of felem_{square,mul}

Add an assembly implementation of felem_{square,mul}, which will be
implemented whenever Altivec support is present and the core implements
ISA 3.0 (Power 9) or greater.

Signed-off-by: Rohan McLure <rohanmclure@linux.ibm.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/21471)