Fix/amu mmap allocation
Created by: mohamedasaker-arm
This change is to fix the following bug:
During amu_mmap_init, struct mod_core_amu_counters array with size
equal to the number of cores that should be allocated.
Instead, an array of struct mod_core_amu_counters pointers
are allocated.
Along with unit tests for AMU counters_base_addr
and counters_offsets