Remove FDT specific parts from INTRNG. Change its interface to make it
universal.

(1) New struct intr_map_data is defined as a container for arbitrary
description of an interrupt used by a device. Typically, an interrupt
number and configuration relevant to an interrupt controller is encoded
in such description. However, any additional information may be encoded
too like a set of cpus on which an interrupt should be enabled or vendor
specific data needed for setup of an interrupt in controller. The struct
intr_map_data itself is meant to be opaque for INTRNG.

(2) An intr_map_irq() function is created which takes an interrupt
controller identification and struct intr_map_data as arguments and
returns global interrupt number which identifies an interrupt.

(3) A set of functions to be used by bus drivers is created as well as
a corresponding set of methods for interrupt controller drivers. These
sets take both struct resource and struct intr_map_data as one of the
arguments. There is a goal to keep struct intr_map_data in struct
resource, however, this way a final solution is not limited to that.

(4) Other small changes are done to reflect new situation.

This is only first step aiming to create stable interface for interrupt
controller drivers. Thus, some temporary solution is taken. Interrupt
descriptions for devices are stored in INTRNG and two specific mapping
function are created to be temporary used by bus drivers. That's why
the struct intr_map_data is not opaque for INTRNG now. This temporary
solution will be replaced by final one in next step.

Differential Revision: https://reviews.freebsd.org/D5730