Expected change is that the XP-640 should print in both color and black and white when using PWG-Raster.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/096104a007d3bf56d3703f26e537635b1c6e5bb7

commit 096104a007d3bf56d3703f26e537635b1c6e5bb7
Author: David Valleau <valleau@chromium.org>
Date: Tue Aug 14 09:13:38 2018

Adding patch to allow PWG Raster types to vary by case

This change adds a patch to CUPS which fixes an issue where Epson
printers would always print in black and white when provided with
pwg-raster, even if the requested print was in colour.

Their reported color scheme was not recognized by CUPS, causing
them to default to black and white.

BUG= chromium:870099 ,  chromium:804990 
TEST=Tested Manually on device

Change-Id: I67473fa41a3a201e6e59312ec17669d8e34bb35a
Reviewed-on: https://chromium-review.googlesource.com/1170082
Commit-Ready: David Valleau <valleau@chromium.org>
Tested-by: David Valleau <valleau@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>

[modify] https://crrev.com/096104a007d3bf56d3703f26e537635b1c6e5bb7/net-print/cups/cups-2.1.4.ebuild
[rename] https://crrev.com/096104a007d3bf56d3703f26e537635b1c6e5bb7/net-print/cups/cups-2.1.4-r51.ebuild
[add] https://crrev.com/096104a007d3bf56d3703f26e537635b1c6e5bb7/net-print/cups/files/cups-2.2.4-case-insensitive-pwg-raster-types.patch