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/cmd_load.c b/common/cmd_load.c
index d043e6d..0aa7937 100644
--- a/common/cmd_load.c
+++ b/common/cmd_load.c
@@ -10,6 +10,7 @@
  */
 #include <common.h>
 #include <command.h>
+#include <console.h>
 #include <s_record.h>
 #include <net.h>
 #include <exports.h>