pinctrl: pass -DDEBUG in subdirs

When drivers are compiled in subdirectories the -DDEBUG flag need
to be passed in the individual Makefiles.

Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Suggested-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>