Adding EPD Feather

[BlitzCityDIY]

Adding EPD Feather support. PR that @ladyada has been testing

[caternuson]

I don't have hardware to test. Generally looks OK, with the nominal fixes for SPI0/SPI1 that @ladyada discovered when testing with actual hardware.

[ladyada]

i tested this UF2 as long as its the one with the crystal-startup-delay thingy!

[BlitzCityDIY]

yes, i did add that to my local install of the pico sdk that is pinned. @caternuson that's where that is defined right?

[caternuson]

The "crystal-startup-delay thingy" would be this:

Local copy of pico-sdk had changes to pico-sdk/src/rp2_common/hardware_xosc/xosc.c:

    xosc_hw->startup = startup_delay * 64;

from here:
#1

In this repo's current state, this is still a required manual step. That is due to the commit point referenced by the pico-sdk submodule (pico-sdk @ fc10a97). It pre-dates this PR:
raspberrypi/pico-sdk#457
which adds a way to configure this without modifying SDK source code. That PR thread also mentions the reason for needing this extra delay.

Suggest making a new issue/PR to address updating the pico-sdk submodule and dealing with startup delay.