boards: arm: Fix XIAO BLE Sense regulator enable gpio pin to use high drive

The XIAO BLE Sense uses a voltage regulator to enable the LSM6DS3TR-C
IMU on it's internal I2C bus. There is an issue where all I2C messages
on this internal bus drop when the `enable-gpio` pin of the voltage
regulator (which powers the IMU) is set to standard drive. Adding the
Nordic flag to set it to use "high drive" for the gpio fixes this.

Signed-off-by: Matthew MacGregor <matthew.macgregor.g@gmail.com>