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/drivers/usb/musb-new/musb_uboot.c b/drivers/usb/musb-new/musb_uboot.c
index 10f6b5d..233a0e4 100644
--- a/drivers/usb/musb-new/musb_uboot.c
+++ b/drivers/usb/musb-new/musb_uboot.c
@@ -1,4 +1,5 @@
 #include <common.h>
+#include <console.h>
 #include <watchdog.h>
 #ifdef CONFIG_ARCH_SUNXI
 #include <asm/arch/usb_phy.h>