media: ti-vpe: cal: Replace context with phy in async notifier entries

The async notifier is meant to bind to subdevs connected to the CSI-2
ports. Those ports are modelled by the CAMERARX phy instances. To
prepare for additional decoupling of contexts and phys, make the
notifier operate on phys. We still initialize and register the context
V4L2 support in the async notifier complete operation as that's our
signal that the userspace API is ready to be exposed.

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