Discuss depopulating unused STM32 and LPC55 crystal oscillators

In Observer #44, we realized that the SP and RoT clock configurations aren't using three of the four crystal oscillators on the PCB:

• The STM32 does not use its 32 kHz crystal oscillator for clock generation
• The LPC55 does not use either of its external crystals for clock generation. It only uses its 96 MHz internal FRO.

This comment contains links to where we configure the STM32 and LPC55 clocks.

We would like to stop populating the unused crystal oscillators on our boards, both to reduce BOM cost and to reduce the number of crystals we have to keep finding alternates for as they go in and out of stock. However, this decision requires buy-in from the hubris team. In this issue, I'd like to have a broader discussion about our long-term hubris clock generation strategy.

Specifically:

• Reiterate (and document) why these clocks were selected
• Get some words down about why we do not use these crystals for clock generation, and whether or not we're going to need them in the future.