IVGCVSW-4400 Backend Counter Registry Functionality
* Adding BackendProfilingContext to the MockBackend
* Made IBackendProfilingContext pure Virtual
* Added UnitTest using MockBackend for testing Backend Counter Registration
* Moved Registry of backend counters from Initialize() to AddBackendProfilingContext()
* Added m_MaxGlobalCounterId to ProfilingService
* Removed automatic registration of MockBack in BackendRegistry()
Signed-off-by: David Monahan <david.monahan@arm.com>
Change-Id: Ie1c6c31e56d1ac7079d6116ecad041961014aedc