drivers: gpio: renesas_rx: Refactor macros for conditional generation

This change introduces GPIO_RX_PORT_IRQ_DECL() and GPIO_RX_PORT_IRQ_ELEM()
macros to conditionally generate GPIO port IRQ declarations and elements
only when the 'port_irq_names' property exists in the device tree node.
This improves code clarity and avoids generating unused code for ports
that do not have IRQ support for Renesas RX

Signed-off-by: Phi Tran <phi.tran.jg@bp.renesas.com>