device property: Introduce fwnode_irq_get()

Until now there were two very similar functions allowing
to get Linux IRQ number from ACPI handle (acpi_irq_get())
and OF node (of_irq_get()). The first one appeared to be used
only as a subroutine of platform_irq_get(), which (in the generic
code) limited IRQ obtaining from _CRS method only to nodes
associated to kernel's struct platform_device.

This patch introduces a new helper routine - fwnode_irq_get(),
which allows to get the IRQ number directly from the fwnode
to be used as common for OF/ACPI worlds. It is usable not
only for the parents fwnodes, but also for the child nodes
comprising their own _CRS methods with interrupts description.

In order to be able o satisfy compilation with !CONFIG_ACPI
and also simplify the new code, introduce a helper macro
(ACPI_HANDLE_FWNODE), with which it is possible to reach
an ACPI handle directly from its fwnode.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>