TEMP: irqchip/irq-pruss-intc: Add an inline pruss_intc_trigger() helper

Add an inline helper pruss_intc_trigger() helper function providing
ease of usage to the PRU client drivers and allow backward compatibility
with the 4.19-based 2019 LTS kernel.

This is only an interim solution and PRU client drivers are expected to
move to invoke the appropriate irqchip function directly.

Signed-off-by: Suman Anna <s-anna@ti.com>