samples: net: echo apps: Add cc2520 configuration for arduino_101

CC2520 is not embedded on an arduino_101, it is however possible to wire
one, and thus it requires to provide cc2520_configure_gpios() function.
This one, being common to a101 is found in samples/net/common.

Change-Id: I86f2734847edb3f6a968522afccc3099ed854d13
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>