ebb: Extend API and bugfixes

This patch adds the extended paf_ebb_pmu_init_ex init API with arguments
to set the pid, cpu and flags.  It also adds a paf_ebb_event_close
function to close the open PMU event file descriptor.

It also adds some internal memory barrier for some API calls.
ebb: Add new testcases

This patch adds new testcases to check for the new extended API.