Draft: Thundercomm db845c (rb3) new device

The Thundercomm Dragonboard 845c aka RB3 is a robotics kit / dev board for the Snapdragon 845 platform. It is the primary device used for usptream development at Linaro (and maybe freedreno too?).

It has 4GB of RAM and 128GB of UFS storage.

TODO:

• Make a wiki page
• Use the common sdm845 kernel package
• switch kernel to makedepends=postmarketos-installkernel, get rid of manual installing of kernel image, use make zinstall (?)
• Get UI too boot (urgh 5.15)