pinctrl: sh-pfc: r8a77990: Add INTC-EX pins, groups and function

Add pins, groups, and function for the Interrupt Controller for
External Devices (INTC-EX) on the R-Car E3 SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>