x86, setup: move isdigit.h to ctype.h, header files on top.

It is a subset of <ctype.h> functionality, so name it ctype.h.  Also,
reorganize header files so #include statements are clustered near the
top as they should be.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4C5752F2.8030206@kernel.org>

arch/x86/boot/compressed/misc.h

@@ -20,6 +20,7 @@
 #include <asm/bootparam.h>
 
 #define BOOT_BOOT_H
+#include "../ctype.h"
 
 /* misc.c */
 extern struct boot_params *real_mode;		/* Pointer to real-mode data */