irqchip: Kconfig: Update description for RENESAS_IRQC config

irq-renesas-irqc driver is also used on Renesas RZ/G{1,2} SoC's, update
the same to reflect the description for RENESAS_IRQC config.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Link: https://lore.kernel.org/r/20200911100439.19878-1-prabhakar.mahadev-lad.rj@bp.renesas.com