Fairly arbitrary mapping of waveform, dither etc :s

Oops

Looks like this is not used as the kernel is using v1 EPDC driver. So
the field is in the struct which is passed to the ioctl but ignored.

Based this mapping mainly on comments from the libremarkable enum, plus
a little wild guesswork.

ALso added a comment pointing to the source for the mxcfb header.

When used as a user-visible string

Currently there is only a single model of reMarkable so it's easy.

(And clang-format pass)

As per libremarkable recommendations.

Now that it's used somewhere else than only on the Libra ;).

Hopefully. The few constants inherited from the kernel are confusing.
According to the libremarkable comments, I'm fairly confident on the A2
mapping here, but the GL16 one only makes sense by virtue of it usually
always being A2 + 1 on all the platforms I'm familiar with...

TL;DR: Here be dragons!

familiar...

A2, at least, appears correct and usable, which is good, as it's the one
most likely to be useful of those two ;).

Also like on other platforms, set the REGAL flag for REAGLD.
Like on other platforms, this is probably a no-op and/or broken ;).

reMarkable