Use correctly-typed external definition for the crash data region, and
eliminate unnecessary pointer indirection.
Results in a small ROM saving even with crash capture disabled, as there
was a pointer for the fault context store in either case. The pointer
isn't needed, as the context store location is fixed according to the
configuration flag.
Added missing mbed_error_initialize function call in bare metal boot code which is used
to retrieve the crash report from RAM in case of any previous abnormal re-boot but this function call is present in RTOS boot code.