memcpy-armv7a.S: Improve performance with misaligned buffers.

Adjust the conditions for entering the aligned copy loop to
improve performance on mutually misaligned buffer copies.

2013-07-01  Will Newton  <will.newton@linaro.org>

	* libc/machine/arm/memcpy-armv7a.S: Adjust entry to
	 aligned loop to improve misaligned copy performance.