refactor(console): move putchar() to console driver

Moving putchar() out of libc and adding a weak dummy
implementation in libc.

This is to remove libc's dependencies to the platform
driver.

Signed-off-by: Claus Pedersen <claustbp@google.com>
Change-Id: Ib7fefaec0babb783def614ea23521f482fa4a28a
diff --git a/lib/libc/putchar.c b/lib/libc/putchar.c
index 037e28a..3472b24 100644
--- a/lib/libc/putchar.c
+++ b/lib/libc/putchar.c
@@ -6,15 +6,9 @@
 
 #include <stdio.h>
 
-#include <drivers/console.h>
-
-int putchar(int c)
+int __putchar(int c)
 {
-	int res;
-	if (console_putc((unsigned char)c) >= 0)
-		res = c;
-	else
-		res = EOF;
-
-	return res;
+	return c;
 }
+
+int putchar(int c) __attribute__((weak,alias("__putchar")));