chore(libc): clean up includes in lib/libc/printf.c

stddef.h is needed for the definition of size_t
stdio.h is needed for the declaration of putchar

Signed-off-by: Jorge Troncoso <jatron@google.com>
Change-Id: I72dac843dbbfc440cff0f9e9d13669b78a812abc
diff --git a/lib/libc/printf.c b/lib/libc/printf.c
index 0def148..e52cbed 100644
--- a/lib/libc/printf.c
+++ b/lib/libc/printf.c
@@ -7,7 +7,9 @@
 #include <assert.h>
 #include <stdarg.h>
 #include <stdbool.h>
+#include <stddef.h>
 #include <stdint.h>
+#include <stdio.h>
 
 #define get_num_va_args(_args, _lcount)				\
 	(((_lcount) > 1)  ? va_arg(_args, long long int) :	\