libc: Add ARMV7 optimized memchr()

 * From Cortex-Strings via Linaro
 * Performance is 10x over the default version on microbenchmarks

Change-Id: I14c1b5ccbd0078219a1dbf9f02fb1591b3a2403c
libc: Remove Scorpion memmove() routine

 * This code is slower than the new implementation under every
   circumstance on Scorpion devices. Remove it and standardize on one
   implementation.
 * Also remove "optimized" memmove_words, which was just a pointer to
   memmove. The performance was identical to the C version on Krait, and
   has regressions on other platforms. This function is only used for
   System.arraycopy in Dalvik.

Change-Id: I42d06fbd7c56d9874b80a0e768dbadf0fa5025a4