arduino_101: add defconfig for mcuboot demonstration

This builds the zephyr OS image with the proper flash offsets for
slot 0.

After building, the image needs to be signed using the zep2newt.py
script included in the MCUBoot repo:

  ./scripts/zep2newt.py --vtoff 0x200 --word-size 4 --sig RSA \
	--key root-rsa-2048.pem --bin <path to zephyr.bin> \
	--out <path to zephyr.bin>

And then run 'make flash'.

Change-Id: I4739c0b7912c8066882208cb450a8224d433965b
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>