Signed-off-by: Rahix <rahix@rahix.de>

These two static variables aren't (and shouldn't!) be used anywhere
outside of bhi160_fetch_fifo() so let's move them into the function.

Signed-off-by: Rahix <rahix@rahix.de>

bhi160_fetch_fifo() doesn't actually return any meaningful error values
anymore.  Remove return-value checks and make the function return void
to express this clearly.

Signed-off-by: Rahix <rahix@rahix.de>

The -EIO error was triggering a warning in the caller.

Also auto generate the header during build time.

Closes #211

Closes #208

Accessory Design Guidelines for Apple Devices says that TX power should
be included in the advertisement.

Also ask for the current time service in the scan report so the card10
shows up in the system dialog.

I don't trust the TRNG/PRNG combo inside the binary blob.

The BLE stack disables the TRNG every time it access it...