Get external SPI SD reader working on M5StickC-Plus

[n0xa]

I wasn't able to get an SD card reader to work with the default SD_CS configuration for the M5StickC-Plus no matter how I wired it up to any of the front pins or Grove port on the back, so I fixed it up.

This change sets up a new single-purpose external SPI bus on the front-panel pins of the M5StickC-Plus. All requisite logic changes are gated in an ifdef specific to the MARAUDER_M5STICKC board target.

A new SPIClass named SPI_EXT is configured. SD_CS is set to -1 since it's unnecessary, as it's the only peripheral on this new SPI bus. Wiring notes in a comment. The wiki will be updated accordingly afrer merge.

Testing results:

• SD Interface is initialized at boot
• SD is green in status bar
• PCAPs are logged to the SD Card
• The lower the battery gets, the more likely the SD Card interface will start flaking out
• Certain SD cards are more tolerant to lower voltages than others. External power recommended
• Evilportal errors if ap.config.txt is missing.
• If index.html and ap.config.txt are present on the SD filesystem, ESP32Marauder crashes with a stack trace. This is likely unrelated to the SD Card and may have something to do with the ESP32-Pico-D4 or some other oddity in this platform's tech stack.

[justcallmekoko]

Can you reconfigure your MR to target merge into the develop branch and resolve any conflicts that come up?

[n0xa]

All set. Cheers.