string: move strdup() & strconcat() to lib/string.c

Move functions not available in PRE_RAM into seperate file.
Makes it easier to share code between rom and ramstage.

Change-Id: I0b9833fbf6742d110ee4bfc00cd650f219aebb2c
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Reviewed-on: https://review.coreboot.org/c/31141
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/lib/string.c

@@ -0,0 +1,21 @@
+#include <string.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+char *strdup(const char *s)
+{
+	size_t sz = strlen(s) + 1;
+	char *d = malloc(sz);
+	memcpy(d, s, sz);
+	return d;
+}
+
+char *strconcat(const char *s1, const char *s2)
+{
+	size_t sz_1 = strlen(s1);
+	size_t sz_2 = strlen(s2);
+	char *d = malloc(sz_1 + sz_2 + 1);
+	memcpy(d, s1, sz_1);
+	memcpy(d + sz_1, s2, sz_2 + 1);
+	return d;
+}