sparc64: shut down to OBP correctly

sparc64: shut down to OBP correctly

Orabug: 23467092

The command "shutdown -h -H now" should shut the system down to the
OBP, however the machine was being powered off in the LDOM case.

In the LDOM case, the "reboot-command" variable must be set to
the string "noop" and then ldom_reboot() must be called.
This will make the OBP ignore the setting of "auto-boot?" after it
completes the reset. This causes the system to stop at the ok prompt.

Signed-off-by: Larry Bassel <larry.bassel@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>