Add basic driver for Waveshare 7.5" e-ink

[jmhobbs]

This is an incomplete, but functional driver for the Waveshare 7.5" e-ink panel, v2

All of their documentation and code refers to it as epd7in5_V2 so I went with roughly that for the names of things.

Currently this only supports full screen draws, and two color (it can handle partial refreshes and a 4-grey mode)

I do intend to come back to those features. I can open a new PR to add features later, or leave this PR open until I get them implemented.

Thanks!

[jmhobbs]

I totally missed the whole waveshare-epd directory 😂

I will shift my work there since there is not a 7.5" version yet.