Introduce two new cache maintainance functions:
* cache_clean_invalidate_data
* cache_invalidate_data
used to flush or invalidate data-cache lines.
Both functions are typically empty, accept for the ARM architecture.
The commit provides implementations for the base-hw kernel, and Fiasco.OC.
Fixes#4207
On ARM, when machine instructions get written into the data cache
(for example by a JIT compiler), one needs to make sure that the
instructions get written out to memory and read from memory into
the instruction cache before they get executed. This functionality
is usually provided by a kernel syscall and this patch adds a generic
interface for Genode applications to use it.
Fixes#1153.
