media: i2c: imx258: Change register settings for variants of the sensor

Sony have advised that there are variants of the IMX258 sensor which
require slightly different register configuration to the mainline
imx258 driver defaults.

There is no available run-time detection for the variant, so add
configuration via the DT compatible string.

The Vision Components imx258 module supports PDAF, so add the
register differences for that variant

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>