lib: string: move strlcpy() to a common place

Move strlcpy() definition from drivers/usb/gadget/ether.c to
lib/string.c because it is a very useful function.
Let's add the prototype to include/linux/string.h too.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/string.c b/lib/string.c
index 29c2ca7..87c9a40 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -102,6 +102,31 @@
 }
 #endif
 
+#ifndef __HAVE_ARCH_STRLCPY
+/**
+ * strlcpy - Copy a C-string into a sized buffer
+ * @dest: Where to copy the string to
+ * @src: Where to copy the string from
+ * @size: size of destination buffer
+ *
+ * Compatible with *BSD: the result is always a valid
+ * NUL-terminated string that fits in the buffer (unless,
+ * of course, the buffer size is zero). It does not pad
+ * out the result like strncpy() does.
+ */
+size_t strlcpy(char *dest, const char *src, size_t size)
+{
+	size_t ret = strlen(src);
+
+	if (size) {
+		size_t len = (ret >= size) ? size - 1 : ret;
+		memcpy(dest, src, len);
+		dest[len] = '\0';
+	}
+	return ret;
+}
+#endif
+
 #ifndef __HAVE_ARCH_STRCAT
 /**
  * strcat - Append one %NUL-terminated string to another