Add a counter to debugfs to count the number of frame-end interrupts.

Link: https://lore.kernel.org/r/20231201140433.2126011-4-paul.elder@ideasonboard.comSigned-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>