Driver definitions which are used by kernel/core in base-hw, and also by other
drivers (e.g. from the os repository) have to reside in the generic
base-repository, for instance some uart drivers. All drivers which are
interesting for one of the sites only (sp804 for timer driver, or
cortex_a9 cpu driver for base-hw) should reside in the respective repos.
Factorize cpu context out of Cortex A9 specific definitions. Moreover, there
is already a Cpu_state object containing all common ARM registers. We use
this as a base for the cpu context switching done by the base-hw kernel.
The Cpu_state class get extended by a cpu-exception field, that stores the kind
of exception raised when the corresponding context got interrupted. This
information is used not only by the base-hw kernel, but also by the TrustZone
VMM that is build currently.
