[gem5] Add support for modeling banks, and add flush latency.

(cherry picked from commit 4a8a4cb0040b4cd547bc62c4ef5f533a7775c5da)

Conflicts:
	gem5-stable/src/mem/SimpleMemory.py
	gem5-stable/src/mem/simple_mem.cc
	gem5-stable/src/mem/simple_mem.hh
	gem5run/run-thnvm-se.sh