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/examples/standalone/mem_to_mem_idma2intr.c b/examples/standalone/mem_to_mem_idma2intr.c
index 215dc22..17da8db 100644
--- a/examples/standalone/mem_to_mem_idma2intr.c
+++ b/examples/standalone/mem_to_mem_idma2intr.c
@@ -28,6 +28,7 @@
 
 
 #include <common.h>
+#include <console.h>
 #include <exports.h>
 
 DECLARE_GLOBAL_DATA_PTR;