Fix a number of bugs in the implementation of writes to the CM_CTRL
system register:
 * write to cm_ctrl, not cm_init !
 * an '&' vs '^' typo meant we would write the inverse of the bits
 * handling the LED via printf() meant we spew lots of output
   to stdout when Linux uses the LED as a heartbeat indicator
 * we would hw_error() if a reset was requested rather than
   actually resetting

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>