Implement a leaner printf for Trusted Firmware

This patch implements a "tf_printf" which supports only the commonly
used format specifiers in Trusted Firmware, which uses a lot less
stack space than the stdlib printf function.

Fixes ARM-software/tf-issues#116

Change-Id: I7dfa1944f4c1e634b3e2d571f49afe02d109a351
diff --git a/lib/stdlib/assert.c b/lib/stdlib/assert.c
index 8156a28..c614854 100644
--- a/lib/stdlib/assert.c
+++ b/lib/stdlib/assert.c
@@ -28,7 +28,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <stdio.h>
+#include <debug.h>
 
 /*
  * This is a basic implementation. This could be improved.
@@ -36,6 +36,6 @@
 void __assert (const char *function, const char *file, unsigned int line,
 		const char *assertion)
 {
-	printf("ASSERT: %s <%d> : %s\n\r", function, line, assertion);
+	tf_printf("ASSERT: %s <%d> : %s\n\r", function, line, assertion);
 	while(1);
 }