ext: update SST test config

Align configuration with new SST change [1] requiring units for
memHierarchy's backend.mem_size parameter.

[1] https://github.com/sstsimulator/sst-elements/commit/c901abb4e79644ff18f5222c94f5dae012772e1e

Change-Id: I19fa09bec8aa453dc52d154598a4ebb20ea304d8

ext: eliminate warnings in SST connector

Now compiles completely clean.

commit 15c633eea52f21dae8cb3a195823b3cdec7be491
Author: Curtis Dunham <Curtis.Dunham@arm.com>
ext: update SST connector for SST 6.0

ext: remove redundant parameter in example SST+gem5 test

The SST connector automatically adds --initialize-only to the gem5
"command line" (as it should); the config script doesn't need it.

config: Support full-system with SST's memory system

This patch adds an example configuration in ext/sst/tests/ that allows
an SST/gem5 instance to simulate a 4-core AArch64 system with SST's
memHierarchy components providing all the caches and memories.