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/common/autoboot.c b/common/autoboot.c
index c367076..c11fb31 100644
--- a/common/autoboot.c
+++ b/common/autoboot.c
@@ -9,6 +9,7 @@
 #include <autoboot.h>
 #include <bootretry.h>
 #include <cli.h>
+#include <console.h>
 #include <fdtdec.h>
 #include <menu.h>
 #include <post.h>