(1) Add a new bus method to get a mapping data for an interrupt.

BUS_MAP_INTR() is used to get an interrupt mapping data according
to provided hints. The hints could be modified afterwards, but only
if mapping data was allocated. This method is intended to be called
before BUS_ALLOC_RESOURCE().

An interrupt mapping data describes an interrupt - hardware number,
type, configuration, cpu binding, and whatever is needed to setup it.

(2) Introduce a method which allows storing of an additional data
in struct resource to be available for bus drivers. This method is
convenient in two ways:

• there is no need to rework existing bus drivers as they can simply be extended to provide an additional data,
• there is no need to modify any existing bus methods as struct resource is already passed to them as argument and thus stored data is simply accessible by other bus drivers.

For now, implement this method only for INTRNG.

This is motivated by needs of modern SOCs where hardware initialization
is not straightforward and resources descriptions are complex, opaque
for everyone but provider, and may vary from SOC to SOC. Typical
situation is that one bus driver can fetch a resource description for
its child device, but it's opaque for this driver. Another bus driver
knows a provider for this kind of resource and can pass this resource
description to it. In fact, something like device IVARS would be
perfect for that if implemented generally enough. Unfortunatelly, IVARS
are usable only by their owners now. Only owner knows its IVARS layout,
thus other bus drivers are not able to use them.

Differential Revision: https://reviews.freebsd.org/D6632