media: i2c: imx258: Add support for 24MHz clock

There's no reason why the clock must be 19.2MHz and nothing
else (indeed this isn't even a frequency listed in the datasheet),
so add support for 24MHz as well.
The PLL settings result in slightly different link frequencies,
so parameterise those.

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