[SYCL][ROCm] Add XFAIL rocm to dep_events.cpp

[AidanBeltonS]

rocm_piextUSMEnqueuePrefetch like cuda_piextUSMEnqueuePrefetch do not currently take flags, so fails with an assert.

Flag feature is waiting on details of Prefetch in USM extension.
Relevant comment from pi_rocm.cpp

// TODO implement handling the flags once the expected behaviour
// of piextUSMEnqueuePrefetch is detailed in the USM extension
  assert(flags == 0u);

USM/prefetch.cpp is currently passing for rocm so is not being set to expected fail.