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>

test/dm/test-main.c

@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <command.h>
+#include <console.h>
 #include <dm.h>
 #include <errno.h>
 #include <malloc.h>

test/dm/usb.c

@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <console.h>
 #include <dm.h>
 #include <usb.h>
 #include <asm/io.h>