use public interface to detect CAS reboots (take 2)

use public interface to detect CAS reboots (take 2)

This is the second pass of this patch.  The fw variable name is changed
to use ibm,client-architecture-support-reboot field which is already present
in the firmware.  Please disregard the previous patch.

The firmware field used to detect CAS reboots (ibm,fw-nbr-reboots) is
really a private field that could change without warning.  A new field
ibm,#reconfig-reboots will be added as a public interface intended to
be used for this detection.  The patch will first check for
ibm,client-architecture-support-reboot if that is not found it will see
if ibm,fw-nbr-reboots is present and will use that instead.

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