media: rkisp1: Acquire pclk clock on i.MX8MP

media: rkisp1: Acquire pclk clock on i.MX8MP

The ISP instances in the NXP i.MX8MP need the input pixel clock to be
enabled in order to access the HDR stitching registers. The clock should
ideally be mandatory, but that would break backward compatibility with
old DT. Try to acquire it as an optional clock instead.

Link: https://lore.kernel.org/r/20250616011115.19515-5-laurent.pinchart@ideasonboard.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>