EDAC, ghes: Gather type-16 'group' handles when walking dimms

Currently ghes_edac exposes all dimms as a flat array. We'd like
to expose more topology as this is particularly useful on NUMA systems.

When we walk the type-17 dimms to gather the dimm handles, we also get
a type-16 'physical memory array' handle. (These replaced the type-5
'memory controller' nodes). We can use this type-16 handle to group
the dimms.

As we count the dimms, allocate as many group structures as we need,
keeping track of the maximum number of dimms found in any one group.

Signed-off-by: James Morse <james.morse@arm.com>