samples: bluetooth: peripheral_hr: add VEGABoard sanity testing
samples: bluetooth: peripheral_hr: add VEGABoard sanity testing

Add a special target that's marked build_only so the BLE SW LL
implementation on VEGABoard is built daily. This helps ensuring
that it doesn't get inadvertedly broken by subsequent updates.
The name of the target is peripheral_hr_rv32m1_vega_ri5cy
and it can be run with the following command:

sanitycheck -v --all -p rv32m1_vega_ri5cy \
            -x=CMAKE_REQUIRED_FLAGS=-Wl,-dT=/dev/null \
            --test samples/bluetooth/peripheral_hr/\
              sample.bluetooth.peripheral_hr_rv32m1_vega_ri5cy

Note: The extra CMake flags are required if running with the official
      VEGABoard compiler, due to this linker issue:
      https://github.com/pulp-platform/pulpino/issues/240

Signed-off-by: Alex Porosanu <9cd4fe7678e1630676677a8799e6ca36cabb4300@nxp.com>

zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr