raspberrypi/boards: add DEFAULT_SD_* for Metro RP2040 and Feather RP2040 Adalogger

Both boards have onboard microSD slots but were missing the
DEFAULT_SD_* pin defines that enable CircuitPython's native SD
automount. Without these, SD-over-USB-MSC only worked via user boot.py
code and hit the heap-mount race in get_vfs().

Pin wiring verified on hardware against the board schematics; CD pin
polarity (DEFAULT_SD_CARD_INSERTED=true) confirmed by runtime test.

Companion to #10963 (automount at filesystem init) and #NNNN (per-LUN
PREVENT_ALLOW response). Fixes the last mile for #10965.