mem: Update DRAM configuration names

Names of DRAM configurations were updated to reflect both
the channel and device data width.

Previous naming format was:
<DEVICE_TYPE>_<DATA_RATE>_<CHANNEL_WIDTH>

The following nomenclature is now used:
<DEVICE_TYPE>_<DATA_RATE>_<n>x<w>
where n = The number of devices per rank on the channel
x = Device width

Total channel width can be calculated by n*w

Example:
A 64-bit DDR4, 2400 channel consisting of 4-bit devices:
n = 16
w = 4
The resulting configuration name is:
DDR4_2400_16x4

Updated scripts to match new naming convention.

Added unique configurations for DDR4 for:
1) 16x4
2) 8x8
3) 4x16

Change-Id: Ibd7f763b7248835c624309143cb9fc29d56a69d1
Reviewed-by: Radhika Jagtap <radhika.jagtap@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>

config: Move the memory instantiation outside FSConfig

This patch moves the instantiation of the memory controller outside
FSConfig and instead relies on the mem_ranges to pass the information
to the caller (e.g. fs.py or one of the regression scripts). The main
motivation for this change is to expose the structural composition of
the memory system and allow more tuning and configuration without
adding a large number of options to the makeSystem functions.

The patch updates the relevant example scripts to maintain the current
functionality. As the order that ports are connected to the memory bus
changes (in certain regresisons), some bus stats are shuffled
around. For example, what used to be layer 0 is now layer 1.

Going forward, options will be added to support the addition of
multi-channel memory controllers.

tests: Add CPU switching tests

This changeset adds a set of tests that stress the CPU switching
code. It adds the following test configurations:

* tsunami-switcheroo-full -- Alpha system (atomic, timing, O3)
* realview-switcheroo-atomic -- ARM system (atomic<->atomic)
* realview-switcheroo-timing -- ARM system (timing<->timing)
* realview-switcheroo-o3 -- ARM system (O3<->O3)
* realview-switcheroo-full -- ARM system (atomic, timing, O3)

Reference data is provided for the 10.linux-boot test case. All of the
tests trigger a CPU switch once per millisecond during the boot
process.

The in-order CPU model was not included in any of the tests as it does
not support CPU handover.