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>

Documentation/devicetree/bindings/media/i2c/sony,imx258.yaml

@@ -13,11 +13,16 @@ description: |-
   IMX258 is a diagonal 5.867mm (Type 1/3.06) 13 Mega-pixel CMOS active pixel
   type stacked image sensor with a square pixel array of size 4208 x 3120. It
   is programmable through I2C interface.  Image data is sent through MIPI
-  CSI-2.
+  CSI-2. The sensor exists in two different models, a standard variant
+  (IMX258) and a variant with phase detection autofocus (IMX258-PDAF).
+  The camera module does not expose the model through registers, so the
+  exact model needs to be specified.
 
 properties:
   compatible:
-    const: sony,imx258
+    enum:
+      - sony,imx258
+      - sony,imx258-pdaf
 
   assigned-clocks: true
   assigned-clock-parents: true