Add support for Raytac MDBT40 module

[nhnifong]

Copies the generic nrf51 and changes the pinout according to the spec for the MDBT40, the module that ships with the XYZrobot 6 DOF Robotic Arm Kit (https://www.pololu.com/product/2743)

I confirmed this allowed me to program one of those modules with an ST-Link V2, flash softdevice 110, and load the serial example. UART communication was working as expected.

[nhnifong]

The script builds when I run locally with ./arduino --verbose-build --verify --board sandeepmistry:nRF5:Raytac_MDBT40 examples/01.Basics/Blink/Blink.ino;

The relevant error from travis seems to be a linker error.

"/home/travis/.arduino15/packages/sandeepmistry/tools/gcc-arm-none-eabi/5_2-2015q4/bin/arm-none-eabi-gcc" "-L/tmp/arduino_build_751411" -Os -Wl,--gc-sections -save-temps "-L/home/travis/Arduino/hardware/sandeepmistry/nRF5/cores/nRF5/SDK/components/toolchain/gcc/" "-L/home/travis/Arduino/hardware/sandeepmistry/nRF5/cores/nRF5/SDK/components/softdevice/{softdevice}/toolchain/armgcc/" "-Tnrf51_{build.chip}.ld" "-Wl,-Map,/tmp/arduino_build_751411/Blink.ino.map" --specs=nano.specs --specs=nosys.specs -mcpu=cortex-m0 -mthumb -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--unresolved-symbols=report-all -Wl,--warn-common -Wl,--warn-section-align -o "/tmp/arduino_build_751411/Blink.ino.elf" "/tmp/arduino_build_751411/sketch/Blink.ino.cpp.o" "/tmp/arduino_build_751411/core/variant.cpp.o" -Wl,--start-group -lm "/tmp/arduino_build_751411/core/core.a" -Wl,--end-group /home/travis/.arduino15/packages/sandeepmistry/tools/gcc-arm-none-eabi/5_2-2015q4/bin/../lib/gcc/arm-none-eabi/5.2.1/../../../../arm-none-eabi/bin/ld: cannot open linker script file nrf51_{build.chip}.ld: No such file or directory

[dlabun]

It's failing in the Travis CI because you didn't specific a chip type in the config file.

[nhnifong]

I've specified the chip for the test. thanks for the help.

[sandeepmistry]

@nhnifong @dlabun any thoughts on my comments from: https://github.com/sandeepmistry/arduino-nRF5/issues/280#issuecomment-410887219

I'm not sure what the advantage of having a separate variant from the generic is for a module. Variants are more intended for developer boards.

[dlabun]

@sandeepmistry Just replied on the #280 thread.

[nhnifong]

I've made the small change. Sorry for not getting to this for two weeks!