boards: arm: support XIAO BLE Sense

This is a variant of XIAO BLE with additional features:
 * LSM6DS3TR-C 6D IMU (3D accelerometer and 3D gyroscope),
 * PDM microphone.

Since LSM6DS3TR-C is almost the same as LSM6DSL (the former has slightly
higher current consumption than the latter, but the register map looks
exactly the same), add devicetree node with "st,lsm6dsl" compatible.

LSM6DS3TR-C is powered directly by P1.08 pin and I2C pull-ups are also
connected to this IO pin. Add a fixed regulator, which will be always on
for this board, in order be able able to use this IMU out of the box.

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>
7 files changed