media: imx: imx8mq-mipi-csi2: Remove unneeded state variable and function

Clean up the driver a bit by inlining the imx8mq_mipi_csi_system_enable()
function to the callsites and removing the hs_settle variable from the
driver state.

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>