openpic: add basic support for MPIC v4.2

Besides the new value in the version register, this provides:
- ILR support, which includes:
  - IDR becoming a pure CPU bitmap, allowing 32 CPUs
  - machine check output support (though other parts of QEMU need to
    be fixed for it to do something other than immediately reboot the
    guest)
- dummy error interrupt support (EISR0/EIMR0 read as zero)
  - actually all FSL MPICs get all summary registers returning zero for now,
    which includes EISR0/EIMR0

Various refactoring is done to support these changes and to ease
new functionality (e.g. a more flexible way of declaring regions).

Just as the code was already not a full implementation of MPIC v2.0,
this is not a full implementation of MPIC v4.2 -- e.g. it still has only
one bank of MSIs.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
