[POWERPC64LE] add mrsas to GENERIC64LE
Approved by: re (gjb)
Reviewed by: bdragon
Sponsored by: Eldorado Research Institute (eldorado.org.br)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D28475
(cherry picked from commit eaffd270d8729c4d79f6ce268275ef4c0e6f7b04)
(cherry picked from commit 928cbdbe39109cdc0075e4cc1a6aa144a8ef8146)