media: cadence: csi2rx: configure DPHY before starting source stream

When the source device is operating above 1.5 Gbps per lane, it needs to
send the Skew Calibration Sequence before sending any HS data. If the
DPHY is initialized after the source stream is started, then it might
miss the sequence and not be able to receive data properly. Move the
start of source subdev to the end of the sequence to make sure
everything is ready to receive data before the source starts streaming.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Fixes: 3295cf12 ("media: cadence: Add support for external dphy")
Tested-by: Julien Massot <julien.massot@collabora.com>
Tested-by: Changhuang Liang <Changhuang.liang@starfivetech.com>
Reviewed-by: Julien Massot <julien.massot@collabora.com>
Reviewed-by: Changhuang Liang <Changhuang.liang@starfivetech.com>
Signed-off-by: Jai Luthra <j-luthra@ti.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>