Put the initialization of the cpu cores, setup of page-tables, enabling of
MMU and caches into a separate component that is only used to bootstrap
the kernel resp. core.
Ref #2092
* name irq controller memory mapped I/O regions consistently
in board descriptions
* move irq controller and timer memory mapped I/O region descriptions
from cpu class to board class
* eliminate artificial distinction between flavors of ARM's GIC
* factor cpu local initialization out of ARM's GIC interface description,
which is needed if the GIC is initialized differently e.g. for TrustZone
Ref #1405
