powerpc/pseries: Implement indexed-count hotplug memory remove

powerpc/pseries: Implement indexed-count hotplug memory remove

BugLink: http://bugs.launchpad.net/bugs/1670315
Indexed-count remove for memory hotplug guarantees that a contiguous block
of <count> lmbs beginning at a specified <index> will be unassigned (NOT
that <count> lmbs will be removed). Because of Qemu's per-DIMM memory
management, the removal of a contiguous block of memory currently
requires a series of individual calls. Indexed-count remove reduces
this series into a single call.

Signed-off-by: Sahil Mehta <sahilmehta17@gmail.com>
Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit 753843471cbbaeca25a5cab51981ee721ad272f7)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>