clk: renesas: r8a779g0: Add INTC-EX clock

Add the module clock used by the Interrupt Controller for External
Devices (INTC-EX) aka IRQC on the Renesas R-Car V4H (R8A779G0) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/8b5ab900ebce8c38604292a5138da11ad2cb072c.1664368268.git.geert+renesas@glider.be