commonlib/bsd: Add strlen() and strnlen() functions

Add strlen() and strnlen() to commonlib/bsd by rewriting them from
scratch, and remove the same functions from coreboot and libpayload.

Note that in the existing libpayload implementation, these functions
return 0 for NULL strings. Given that POSIX doesn't require the NULL
check and that other major libc implementations (e.g. glibc [1]) don't
seem to do that, the new functions also don't perform the NULL check.

[1] https://github.com/bminor/glibc/blob/master/sysdeps/i386/strlen.c

Change-Id: I1203ec9affabe493bd14b46662d212b08240cced
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83830
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/lib/string.c

@@ -33,22 +33,6 @@ char *strconcat(const char *s1, const char *s2)
 	return d;
 }
 
-size_t strnlen(const char *src, size_t max)
-{
-	size_t i = 0;
-	while ((*src++) && (i < max))
-		i++;
-	return i;
-}
-
-size_t strlen(const char *src)
-{
-	size_t i = 0;
-	while (*src++)
-		i++;
-	return i;
-}
-
 char *strchr(const char *s, int c)
 {
 	do {