libc: krait: Re-factor high-performance memcpy for thumb2

The majority of libc under bionic is built for thumb2.  Refactor the
high performance memcpy used in previous builds for thumb2, including
information that can be used for stack-unwinding.

Change-Id: Ib5f7ab354f39313758402ec02b0aea27b15d45fa
1 file changed