Intel RDT: fix compilation with libpqos < 4.4.

[octo]

Currently the compilation fails on a number of systems with the following error:

  CC       src/intel_rdt_la-intel_rdt.lo
../../src/intel_rdt.c: In function 'rdt_config_events':
../../src/intel_rdt.c:49:54: error: 'PQOS_PERF_EVENT_LLC_REF' undeclared (first use in this function); did you mean 'PQOS_PERF_EVENT_LLC_MISS'?
    PQOS_MON_EVENT_TMEM_BW | PQOS_MON_EVENT_RMEM_BW | PQOS_PERF_EVENT_LLC_REF)
                                                      ^~~~~~~~~~~~~~~~~~~~~~~
../../src/intel_rdt.c:568:13: note: in expansion of macro 'RDT_EVENTS'
   events &= RDT_EVENTS;
             ^~~~~~~~~~
../../src/intel_rdt.c:49:54: note: each undeclared identifier is reported only once for each function it appears in
    PQOS_MON_EVENT_TMEM_BW | PQOS_MON_EVENT_RMEM_BW | PQOS_PERF_EVENT_LLC_REF)
                                                      ^~~~~~~~~~~~~~~~~~~~~~~
../../src/intel_rdt.c:568:13: note: in expansion of macro 'RDT_EVENTS'
   events &= RDT_EVENTS;
             ^~~~~~~~~~
make[2]: *** [Makefile:8133: src/intel_rdt_la-intel_rdt.lo] Error 1

ChangeLog: Intel RDT plugin: A compatibility issue with pqos < 4.4 has been fixed.