drmgr: Use sysfs migration store to initiate migration when possible
drmgr: Use sysfs migration store to initiate migration when possible

The sysfs attribute /sys/kernel/mobility/migration has been present for
sometime, but never actually used by drmgr. It can be used to initiate a
migration operation in place of the existing faux ibm,supsend-me rtas call.
Further, newer kernels are capable of doing the device tree update.

We can test the /sys/kernel/mobility/api_version attribute to determine the
course of action drmgr should take. Newer kernels will return 1 indicating
the kernel is cabable of performing the migration and postmobility fixups.
If the attribute is unreadable or returns 0 drmgr should resort to initiating
the migration via rtas, and communicate the post mobility device tree update
through the /proc/ppc64/ofdt interface to the kernel.

Signed-off-by: Tyrel Datwyler <f4a317f2a73d762775eb462a22d913f1ae21c433@linux.vnet.ibm.com>

kamalesh-babulal/powerpc-utils,mdroth/powerpc-utils,mdroth/powerpc-utils,kamalesh-babulal/powerpc-utils,shenki/powerpc-utils,shenki/powerpc-utils,mdroth/powerpc-utils,kamalesh-babulal/powerpc-utils,shenki/powerpc-utils