media: i2c: adv748x: Convert SW reset routine to function

The ADV748x is currently reset by writting a small table of registers to
the device.

The table lacks documentation and contains magic values to perform the
actions, including using a fake register address to introduce a delay
loop.

Remove the table, and convert to code, documenting the purpose of the
specific writes along the way.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>