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>