media: i2c: isl7998x: Add driver for Intersil ISL7998x

Add driver for the Intersil ISL7998x Analog to MIPI CSI-2/BT656 decoder.
This chip supports 1/2/4 analog video inputs and converts them into
1/2/4 VCs in MIPI CSI2 stream.

This driver currently supports ISL79987 and both 720x480 and 720x576
resolutions, however as per specification, all inputs must use the
same resolution and standard. The only supported pixel format is now
YUYV/YUV422. The chip should support RGB565 on the CSI2 as well, but
this is currently unsupported.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
To: linux-media@vger.kernel.org
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[Sakari Ailus: Always call pm_runtime_get_and_resume in pre_streamon]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>