Zephyr nordic: assign SPIM3 as first busio.SPI() bus #11599

• Addressed in zephyr-cp: dynamic buses on the Feather nRF52840 boards #11576

Zephyr is assigning SPIM2 before SPIM3. SPIM3 can run at 32 MHz, and the other SPIMs run at only 8 MHz. Assign SPIM3 first. This replicates the ports/nordic behavior.

The fix is to sort the SPIMs by frequency.

Note: In ports/nordic we had to work around some SPIM3 errata, including by allocating a block of RAM for its use. The nrfx used in zephyr does a better job of this, and we don't have to do it ourselves.