chore(Makefile): fix a mkdir problem under old make versions

Under old make version, the trailing slash in a dependency is ignored,
also a rule with a target like

  %/:
          mkdir -p $@

will not work because the trailing slash will never be found.
Instead of this rule, the directory related dependencies are genrated
during the MKDEP.
feat(xenperf): add AMD family 16 performance counter support

Refactor the perfcnt structure to make it object-oriented (vcall map)
Add a coremap to find the node for each core.
Add the northbridge event support for AMD family 16 (tested on Magny
Cour).
Merge branch 'xenperf-refactor'