[media] omap4iss: Remove VIDEO_OMAP4_DEBUG Kconfig option

The option was supposed to control the definition of the DEBUG macro in
the Makefile but has been left unused by mistake. Given that debugging
should be enabled using dynamic printk, remote the Kconfig option.

[Reworked the commit message]

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>