olimex_a20_olinuxino_lime2: new board

It is based on olimex_a20_olinuxino_lime configuration. Tested on the mainline
kernel 4.1.4. It boots and the Ethernet is working at speed 1 Gbps.

[Thomas: remove ccache and optimize 2 options.]

Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
Acked-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>