SCP: Stop calls VM-provided address printer for PC without REG_VMAD from Dave Bryan

OBSERVATION:  For a simulator stop, sim_vm_fprint_addr (if defined) is
     called to print the value of the program counter, regardless of whether or
     not the register was defined with REG_VMAD.  However, displaying the PC
     value with "examine" calls sim_vm_fprint_addr only if the REG_VMAD flag is
     present.  The displayed value of the PC should be the same in both cases.