DEBUG: Fix debug macros

The current implementation of debug doesn't play well with GCC4.6.
This implementation also fixes GCC4.6 complaints about unused variables
while maintaining code size.

Also, drop the debugX() as that's not used anywhere anymore.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>