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_fastboot.c b/common/cmd_fastboot.c
index b9d1c8c..488822a 100644
--- a/common/cmd_fastboot.c
+++ b/common/cmd_fastboot.c
@@ -9,6 +9,7 @@
  */
 #include <common.h>
 #include <command.h>
+#include <console.h>
 #include <g_dnl.h>
 #include <usb.h>