pinctrl: sh-pfc: r8a7796: Deduplicate VIN4 pin definitions

Use union vin_data and VIN_DATA_PIN_GROUP() to reduce redundancies
in pin definitions.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>