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_pci.c b/common/cmd_pci.c
index dcecef8..802e433 100644
--- a/common/cmd_pci.c
+++ b/common/cmd_pci.c
@@ -17,6 +17,7 @@
 #include <bootretry.h>
 #include <cli.h>
 #include <command.h>
+#include <console.h>
 #include <asm/processor.h>
 #include <asm/io.h>
 #include <pci.h>