[media] media: imx: Add MIPI CSI-2 Receiver subdev driver

Adds MIPI CSI-2 Receiver subdev driver. This subdev is required
for sensors with a MIPI CSI2 interface.

- Switch from the v4l2_of_ APIs to the v4l2_fwnode_ APIs.
- Add the function csi2ipu_gasket_init() to initialize the gasket at
  s_power(ON). The gasket needs to be programmed with the correct color
  component ordering to handle UYVY vs. YUYV ordered mbus formats from
  sensors. Note that the description of the CSI2IPU_GASKET register in
  the i.MX6 reference manual is wrong w.r.t bit 2 (the manual refers to
  this register as CSI2_SW_RST): setting bit 2 selects YUYV order, not UYVY.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Suggested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>