* Convert to SDK RP2350A/B determination
Fixes#2878
The SDK uses `defined(PICO_RP2350) && !PICO_RP2350A` to indicate an RP2350B
chip, not the define PICO_RP2350B.
Match the SDK's usage by converting from `defined(PICO_RP2350B)` to
`defined(PICO_RP2350) && !PICO_RP2350A` and update the chip variants
accordingly.
* Need to explicitly override PICO_RP2350A for all
The *SDK*'s board definition file hardcodes a PICO_RP2350A value for
all boards, but we use the same board file for both A and B variants.
Override the SDK board definition in the variant definition file.
* Generic RP2350 needs 2-stage PICO_RP2350A setting
Also ensure SDK board definition included before pins_arduino.h for
clearing up redefinition errors.
* Factor out undef PICO_RP2350A
* Update Arduino.h
