The Atmel ISC driver will be moved to staging to support old users that
are not using the media controller paradigm.
The ISC driver was converted to media controller in the public patch
series:

https://lore.kernel.org/lkml/20220503095127.48710-1-eugen.hristev@microchip.com/T/#m2c320fa8153c01379a1c35b1d90a00903949513a

However the conversion cannot be done directly as it would affect existing
users by breaking the old way of configuration for sama5d2 platforms.

After discussions with the media maintainers, the decision is to move
Atmel ISC to staging as-is, to keep the Kconfig symbols and the users
to the driver in staging. Thus, all the existing users of the non
media-controller paradigm will continue to be happy and use the old config
way.

The converted driver would support both sama5d2 and sama7g5 platforms with
media controller paradigm, but it requires userspace configuration of the
pipeline for all the pipeline modules.

In a simple configuration sensor ==> isc , the old isc driver used to call
subdev s_fmt and control the sensor directly.
This was achieved by having a lot of code inside the driver that was
querying the subdev at probe time and made a list of formats which are
usable.
Basically the user had nothing to configure, as the isc would handle
everything at the top level. This was an easy way to capture, but also came
with the drawback of lack of flexibility.
In a more complicated pipeline
 sensor ==> controller 1 ==> controller 2 ==> isc
this would not be achievable, as controller 1 and controller 2 might be
media-controller configurable, and will not propagate the formats down to
the sensor.
The new driver Microchip ISC would solve all these problems and exposes pads
entities and links to userspace.
For the ease of tracking, the patches that convert to media controller come
on top of this patch that simply readds the driver to the new location under
the new Kconfig symbols.

To differentiate between the old driver and the new driver, I have renamed
the new driver to Microchip ISC, renaming the Kconfig symbols as well, and
all the mentions inside the driver.
The only thing that remains common is the file
include/linux/atmel-isc-media.h which is the ABI for the v4l2 custom
controls that the ISC exposes.
This file is used by both driver, so I kept it as-is.
To further avoid confusion all files have been renamed and all functions
named isc_* as well.
The exported symbols have been renamed with added microchip_ prefix, to
avoid symbol duplication with the old driver, and to avoid confusion.
Other than that, I have fixed small checkpatch issues when readding the
driver.
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>