media: rkisp1: debug: Add debugfs files to dump core and ISP registers

It's useful to dump the value of registers for debugging purpose. Add
two debugfs files to dump key core and ISP registers.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>