media: imx-pxp: detect PXP version

Different versions of the Pixel Pipeline have different blocks and their
routing may be different. Read the PXP_HW_VERSION register to determine
the version of the PXP and print it to the log for debugging purposes.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>