media: imx: imx7_mipi_csis: Calculate Ths_settle from source lane rate

The Ths_settle timing parameter depends solely on the lane data rate of
the source. Calculate it at runtime instead of requiring it to be
specified in the device tree.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>