* Keep MPU_PWR low when the sensor is not in use
* Deselect the sensor when not in use, in order to restore the I2C ping state
* Explicitly control the MPU_INT pin
* Don't shutdown the sensor when it's shut down
* Remove explicit shutdown-related API extension. It is no longer required
Instead of using a separate data structure to request that a PD remain powered during deep sleep,
we do the same within the main LPM data structure through an additional field.
This allows us to maintain only one linked list of LPM modules and overall improves code clarity
We only power, clock and enable the peripepheral when / if we need it
* We no longer automatically turn on the SERIAL PD when the CM3 is running
* Make sure the I2C peripheral is accessible (powered and clocked) before any operation
* If the peripheral is not accessible, automatically power it up and run the clock
* Put SDA, SCL, SDA HP and SCL HP in a low-leakage state when shutting down
* Don't automatically fire up the I2C controller when we wake up
* Explicitly put in deep sleep on device startup
* Verify that the flash has actually dropped to deep sleep
* Update CLK pin to match the one used on the v1.2 sensortag
Obsoletes and Closes#988
