Spi enhancements

[jepler]

This required both adding support for the "default write value" in bitbangio.SPI, and also supporting duck-typing in adafruit_bus_device's SPIDevice which, surprisingly, was overlooked when we fixed I2C.

Now, the following code works, tested on RT1010-EVK:

import os
import board
import bitbangio
import adafruit_sdcard
import storage
import digitalio

spi = bitbangio.SPI(board.SCK, MISO=board.MISO, MOSI=board.MOSI)
cs = board.D10
sdcard = adafruit_sdcard.SDCard(spi, digitalio.DigitalInOut(cs))
vfs = storage.VfsFat(sdcard)
storage.mount(vfs, "/sd")
print(os.listdir("/sd"))

Closes #4494.

[gamblor21]

Looks good to me. I haven't tested it, I can try just have to see if I have a display with an SD card on the back laying about somewhere.

[ladyada]

will test when there's artifacts!

[ladyada]

verified with a TFT shield on a metro m7!

[ladyada]

also verified with a teensy 4.1's SDIO card slot