media: rkisp1: Compile debugfs support conditionally

When CONFIG_DEBUGFS is disabled, there's no need to compile the debugfs
support in. Make it conditional.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Dafna Hirschfeld <dafna@fastmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>