bug#36551: [META] Run Guix System on Purism Librem 5

[Jonathan Brielmaier]

This is a meta/tracker bug to track what needs to be done and what is
already done, to run Guix system on the Purism Librem 5 phone.
https://puri.sm/products/librem-5/

The Librem 5 will be shipped with a mobile optimized GNOME based on
PureOS which is based on Debian, but contains only free software :)

As the phone and the software is still in heavy development, we don't
know yet what exactly is required to have a proper "phone" experience.

Hardware spec:
SoC: NXP iMX8M Quad Core
arch: aarch64
storage: 32GB eMMC
For more details see: https://shop.puri.sm/shop/librem-5/

GNOME and it's packages should be on the newest versions, as they could
contain fixes and improvements for a mobile UI (responsive).

The following packages are still missing in Guix or may need adjustments.

Kernel/boot:
- kernel: At the moment there are surely patches on top of linux-vanilla
  required, but Purism pushes hard to upstream those. So maybe no
special  is required when the phones ship.
- u-boot-imx: U-Boot for iMX, they have still patches on top of
  https://source.codeaurora.org/external/imx/uboot-imx

Core libraries:
- libhandy: provides responsive UI stuff for GTK, may becoming
dependency of some GNOME packages https://source.puri.sm/Librem5  /libhandy
- phosh: Wayland shell (prototype) for GNOME on mobile devices:
  https://source.puri.sm/Librem5/phosh

Leaf packages:
- calls: App for calling, backend ModemManager or oFono
  https://source.puri.sm/Librem5/calls
- chatty: App for SMS and XMPP messaging:
  https://source.puri.sm/Librem5/chatty
- epiphany/GNOME Web: They have some patches for mobile UI:
  https://source.puri.sm/Librem5/epiphany
- gnome-contacts: Missing in Guix, they have a phone-focused fork:
  https://source.puri.sm/Librem5/gnome-contacts

Feel free to add comments, other bugs which are related or relevant
links etc.