drivers: interrupt_controller: Add driver for NXP's IRQ_STEER IP

This commit introduces a new interrupt controller driver used
for NXP's IRQ_STEER IP.

Apart from introducing the driver itself, this commit contains
the following changes:
	1) Switch i.MX8MP to using the XTENSA core interrupt
	controller instead of the dummy irqsteer one.
		* this is required because the binding for the
		irqsteer driver is no longer a dummy one
		(since it's being used by the irqsteer driver).
		As such, to avoid having problems, switch to
		using another dummy binding.
	2) Modify the irqsteer dummy binding such that it
	serves the IRQ_STEER driver's needs.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>