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/Arcturus/ucp1020/spl.c b/board/Arcturus/ucp1020/spl.c
index 236b0d0..9315bb7 100644
--- a/board/Arcturus/ucp1020/spl.c
+++ b/board/Arcturus/ucp1020/spl.c
@@ -9,6 +9,7 @@
  */
 
 #include <common.h>
+#include <console.h>
 #include <ns16550.h>
 #include <malloc.h>
 #include <mmc.h>