ARM: shmobile: sh73a0 dtsi: Add missing INTCA0 clock for irqpin module

This clock drives the irqpin controller modules.
Before, it was assumed enabled by the bootloader or reset state.
By making it available to the driver, we make sure it gets enabled when
needed, and allow it to be managed by system or runtime PM.

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