irqchip/irq-pruss-intc: Implement irq_{get, set}_irqchip_state ops

This implements the irq_get_irqchip_state and irq_set_irqchip_state
callbacks for the TI PRUSS INTC driver. The set callback can be used
by drivers to "kick" a PRU by injecting a PRU system event.

Co-developed-by: Suman Anna <s-anna@ti.com>
Co-developed-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
Reviewed-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>