sim: mcore: pull cpu state out of global scope

sim: mcore: pull cpu state out of global scope

This avoids using global variables to hold the cpu state so we can
better integrate with the sim common code.

There's also a minor fix here where we move the pc register back into
the state that is accessible by the asints array.  When it was pulled
out previously, the reg store/fetch functions broke, but no one really
noticed as the mcore gdb port was dropped a while back.