Add initial DPAA2 support

DPAA2 is a hardware-level networking architecture found in some NXP
SoCs which contain hardware blocks including Management Complex
(MC, a command interface to manipulate DPAA2 objects), Wire Rate I/O
processor (WRIOP, packets distribution, queuing, drop decisions),
Queues and Buffers Manager (QBMan, Rx/Tx queues control, Rx buffer
pools) and the others.

The Management Complex runs NXP-supplied firmware which provides DPAA2
objects as an abstraction layer over those blocks to simplify an
access to the underlying hardware. Each DPAA2 object has its own
driver (to perform an initialization at least) and will be visible
as a separate device in the device tree.

Two new drivers (dpaa2_mc and dpaa2_rc) act like firmware buses in
order to form a hierarchy of the DPAA2 devices:

acpiX (or simplebusX)

	  dpaa2_mcX
	    dpaa2_rcX
	      dpaa2_mcp0
	      ...
	      dpaa2_mcpN
	      dpaa2_bpX
	      dpaa2_macX
	      dpaa2_io0
	      ...
	      dpaa2_ioM
	      dpaa2_niX

dpaa2_mc is suppossed to be a root of the hierarchy, comes in ACPI
and FDT flavours and implements helper interfaces to allocate and
assign bus resources, MSI and "managed" DPAA2 devices (NXP treats some
of the objects as resources for the other DPAA2 objects to let them
function properly). Almost all of the DPAA2 objects are assigned to
the resource containers (dpaa2_rc) to implement isolation.

The initial implementation focuses on the DPAA2 network interface
to be operational. It is the most complex object in terms of
dependencies which uses I/O objects to transmit/receive packets.

Approved by: bz (mentor)
Tested by: manu, bz
MFC after: 3 months
Differential Revision: https://reviews.freebsd.org/D36638