mb/google/volteer/var/voxel: Add memory parts and generate DRAM IDs

mb/google/volteer/var/voxel: Add memory parts and generate DRAM IDs

This change adds memory parts used by variant voxel to
mem_list_variant.txt and generates DRAM IDs allocated to these parts.
This variant is not yet supported by coreboot but DRAM IDs need to be
generated for it. In the coming days, variant voxel will be added to
coreboot.

BUG=b:157732528

Change-Id: I8780beec987deb8fed11bb8f84275dcba4768514
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41994
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>