epicardium: Query BLE hardware for idle periods

Query the BLE base band for idle periods and put the CPU to sleep during this time. This allows us to reduce clock speed again and wake up in time to quickly serve BLE interrupts.

In the future we can now even go lower than DIV4, as BLE continues to work at least until DIV16.

Looks good to me! Thanks for keeping our codebase clean.

However, I'm only a bot - so a human will still have to approve this request.

merged

mentioned in commit 4b22f2a7