Revert "removed arch armv7 opt"

This reverts commit 1708bc40fcf7fc064e22a7c8e9e946e019967bb3.
Revert "ARM: Use -mcpu=cortex-a15 when targeting MSM Krait CPUs"

This reverts commit 743dfd4e0e29c5db5778dbaf24672d1b63b679fb.