Revert "Disable -mcpu=cortex-a15 flag for krait"

This reverts commit d3694caec8b51697c5afd76a3da0f550352ae3dd.

Change-Id: I1b2586b12136026cbde8bca9995a58d891ed908f

Conflicts:
	core/combo/arch/arm/armv7-a-neon.mk