The vanilla NOVA kernel solely supports tracking and exporting of execution
times per SC kernel object, but not per thread (EC object). The commit extends
to track execution times per EC in the NOVA kernel, exporting it to Genode's
'core' roottask and populating Genode's Trace::Subject_info structure.
Fixes#4481
Instead of holding SPEC-variable dependent files and directories inline
within the repository structure, move them into 'spec' subdirectories
at the corresponding levels, e.g.:
repos/base/include/spec
repos/base/mk/spec
repos/base/lib/mk/spec
repos/base/src/core/spec
...
Moreover, this commit removes the 'platform' directories. That term was
used in an overloaded sense. All SPEC-relative 'platform' directories are
now named 'spec'. Other files, like for instance those related to the
kernel/architecture specific startup library, where moved from 'platform'
directories to explicit, more meaningful places like e.g.: 'src/lib/startup'.
Fix#1673
