platform/mulle: Add stub for button_sensor.

We do not have any buttons on the board but some of the Contiki
examples expect the functions in dev/button-sensor.h to exist and to
provide a sensor called button_sensor.

The implementation is copied straight from platform/native.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Add empty compatibility uart1.h

This file exists simply to make some broken examples (rpl-border-router
etc.) that are dependent on platform specific headers compile correctly.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Sanitise GDB command line for upload

Generate a new temporary file for each invokation of the upload target.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
examples/ipv6/rpl-border-router: Add -DUIP_CONF_TCP=1 to CFLAGS

The example used to rely on the default value being set to 1 which
caused build failures on platforms which have a default UIP_CONF_TCP=0

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>