ARM OMAP2+ GPMC: don't undef DEBUG

OMAP2+ GPMC driver undefines DEBUG, which makes it unnecessarily
hard to turn DEBUG on. Remove the offending lines.

Signed-off-by: Robert ABEL <rabel@cit-ec.uni-bielefeld.de>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>