Fix define MBED_EXCLUSIVE_ACCESS for Apple M1 (ARM64) computers
Fix define MBED_EXCLUSIVE_ACCESS for Apple M1 (ARM64) computers

The new Apple M1 Mac computers are ARM based. When compiling and running
unit tests on an M1 Mac, the architecture is defined as __arm__

An extra check for __aarch64__ is needed to set MBED_EXCLUSIVE_ACCESS to 0U for the M1
Mac

If not, compilation fails with "Unknown ARM architecture for exclusive access" error

mbedmicro/mbed,mbedmicro/mbed,mbedmicro/mbed,mbedmicro/mbed,mbedmicro/mbed