This bug was introduced in c310a1e9 and was
breaking bfk3 builds ever since.

This rule file is packaged in fbset-modes-sm750-bfk3 since 2.0.

This package includes some common configuration
we use for BE-T1000 based boards.

sm750 is seen as framebuffer-only device, so it's not marked with
master-of-seat tag with current udev (which does this mostly to
dri cards). But without master-of-seat device logind does not
report that the seat "CanGraphical", and thus sddm does not
work for it; there might be other problems, too.

This change adds udev rule that marks sm705's fb device as
master-of-seat.

We only plan to distribute XZ-compressed rootfs tarballs.

(mike@: merging cleaned-up version)