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/cobra5272/flash.c b/board/cobra5272/flash.c
index c0b8337..4fac688 100644
--- a/board/cobra5272/flash.c
+++ b/board/cobra5272/flash.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <console.h>
 
 #define PHYS_FLASH_1 CONFIG_SYS_FLASH_BASE
 #define FLASH_BANK_SIZE 0x200000