scripts:nrf: Add 'make flash' for nrf boards.

Tested on nrf52_pca10040 and nrf51_pca10028 using hello_world sample.

Change-Id: I7cdf1d21e7f8232da737a06e5afbfb1eaec05cde
Signed-off-by: Michał Kruszewski <mkru1992@gmail.com>
4 files changed