powerpc/drmem: Add support for ibm, dynamic-memory-v2 property

The Power Hypervisor has introduced a new device tree format for
the property describing the dynamic reconfiguration LMBs for a system,
ibm,dynamic-memory-v2. This new format condenses the size of the
property, especially on large memory systems, by reporting sets
of LMBs that have the same properties (flags and associativity array
index).

This patch updates the powerpc/mm/drmem.c code to provide routines
that can parse the new device tree format during the walk_drmem_lmb*
routines used during boot, the creation of the LMB array, and updating
the device tree to create a new property in the proper format for
ibm,dynamic-memory-v2.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>