arm64: lib: Implement optimized string compare routines

This patch, based on Linaro's Cortex Strings library, adds
an assembly optimized strcmp() and strncmp() functions.

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 --git a/arch/arm64/include/asm/string.h b/arch/arm64/include/asm/string.h
index 3a43305..6133f49 100644
--- a/arch/arm64/include/asm/string.h
+++ b/arch/arm64/include/asm/string.h
@@ -22,6 +22,12 @@
 #define __HAVE_ARCH_STRCHR
 extern char *strchr(const char *, int c);
 
+#define __HAVE_ARCH_STRCMP
+extern int strcmp(const char *, const char *);
+
+#define __HAVE_ARCH_STRNCMP
+extern int strncmp(const char *, const char *, __kernel_size_t);
+
 #define __HAVE_ARCH_MEMCPY
 extern void *memcpy(void *, const void *, __kernel_size_t);