Move console definitions into a new console.h file

The console includes a global variable and several functions that are only
used by a small subset of U-Boot files. Before adding more functions, move
the definitions into their own header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/lwmon5/kbd.c b/board/lwmon5/kbd.c
index 97962da..d6c0a20 100644
--- a/board/lwmon5/kbd.c
+++ b/board/lwmon5/kbd.c
@@ -17,6 +17,7 @@
 #include <common.h>
 #include <i2c.h>
 #include <command.h>
+#include <console.h>
 #include <post.h>
 #include <serial.h>
 #include <malloc.h>