boards: arm: particle_*: enable PCB antenna on startup

All three boards use a Skyworks SPDT switch to control whether the
antenna is connected to a PCB antenna or an external u.FL connector.
None of them power up in a state that properly enables an antenna.
Add startup code to configure for the PCB antenna.

Fixes: https://github.com/zephyrproject-rtos/zephyr/issues/14123



Signed-off-by: Peter A. Bigot <pab@pabigot.com>
[mike@foundries.io: adjusted code to use Zephyr GPIO APIs.  boron is
now also based on DTS.]
Signed-off-by: Michael Scott <mike@foundries.io>