media: rkisp1: debug: Collect input status by sampling ISP_FLAGS_SHD

The ISP_FLAGS_SHD register exposes the ISP parallel input signals (data
and synchronization) in real time. This can help debugging when the
device doesn't output any image. Sample the register 10000 times with a
1µs delay and expose the result through debugfs.

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>