arm64: lib: Implement optimized memcmp routine

This patch, based on Linaro's Cortex Strings library, adds
an assembly optimized memcmp() function.

Signed-off-by: Zhichang Yuan <zhichang.yuan@linaro.org>
Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --cc arch/arm64/include/asm/string.h
Simple merge

diff --cc arch/arm64/kernel/arm64ksyms.c
Simple merge

diff --cc arch/arm64/lib/Makefile
Simple merge

diff --cc arch/arm64/lib/memcmp.S
Simple merge