pinctrl: sh-pfc: Reduce kernel size for narrow VIN channels

Some VIN channels support less than 24 lanes.  As union vin_data always
consumes space for 24 lanes, this wastes memory.

Hence introduce new smaller unions vin_data12 and vin_data16, to
accommodate VIN channels with only 12 or 16 lanes.

This reduces the static pin controller driver size by 320 bytes for
R-Car V2H, and by 96 bytes for R-Car E2.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>