hw/arm/virt: Merge VirtBoardInfo and VirtMachineState

hw/arm/virt: Merge VirtBoardInfo and VirtMachineState

One of the purposes of VirtBoardInfo was to hold various
bits of state about the board. Now we have MachineState
and the subclass VirtMachineState to do this. Fold the
VirtBoardInfo into VirtMachineState rather than having
some flags in one struct and some in another with no
useful way to get between them.

In the process we drop the code for looking up the
memory map and irq map from the CPU model, because
in practice we always use the same maps in all cases.

For easier code review, this change removes the
VirtBoardInfo type but leaves all the variables which
used to be VirtBoardInfo* and are now VirtMachineState*
with their now-confusing 'vbi' names.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>