dt-bindings: media: imx258: Add alternate compatible strings

There are a number of variants of the imx258 modules that can not
be differentiated at runtime, so add compatible strings for the
PDAF variant.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Luis Garcia <git@luigi311.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>