Faster startup when BOD is selected for the 328

[cburstedde]

I've added logic to boards.txt such that with BOD enabled the faster SUT settings are used. This is in accordance with the 328 and 328PB spec sheets. The difference is about 1/15 seconds, which is noticeable when squinting hard.

Tested with 18.432 MHz external and 8 and 1 MHz internal both with BOD 2.7 and disabled.

I don't have Platform IO installed, so I have not added the feature there.