Revert "Revert "Specify -mcpu=cortex-a15 for krait CPU variants.""

Hlte uses pre-build mount.exfat so restore a15 flag

This reverts commit 87b26fab775f819375453f65e5dece063045b56e.

(cherry picked from commit 89fb19de98ca83241ca9f8e3d65e0a0624a56d51)