Add support for the Raspberry Pi PiSP Back End.

The driver has been upported from the Raspberry Pi kernel at revision
f74893f8a0c2 ("drivers: media: pisp_be: Update seqeuence numbers of the
buffers").

The ISP documentation is available at:
https://datasheets.raspberrypi.com/camera/raspberry-pi-image-signal-processor-specification.pdfSigned-off-by: David Plowman <david.plowman@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.org>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil: drop dev_err after platform_get_irq to fix a coccinelle check]