This patch adds support for some HW version of the TP-Link TL-WR841 with
an upgrade to 8MB or 16MB flash.

This patch was adapted from the Freifunk Hannover site:
https://github.com/freifunkh/site/blob/master/patches/0003-added-TP-Link-TL-WR841ND-N-Devices-for-8M-and-16M-Va.patch


from revision 8fdc73456f3b47418dab613cff7c70347b6b8c40.

Since FFH's patch is intended for gluon master this patch is adapted to
gluon-v2018.2.x's build system.

Signed-off-by: Chris Fiege <chris@tinyhost.de>