media: i2c: imx258: Support faster pixel rate on binned modes

With the binned modes, there is little point in faithfully
reproducing the horizontal line length of 5352 pixels on the CSI2
bus, and the FIFO between the pixel array and MIPI serialiser
allows us to remove that dependency.

Allow the pixel array to run with the normal settings, with the MIPI
serialiser at half the rate. This requires some additional
information for the link frequency to pixel rate function that
needs to be added to the configuration tables.

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