postmarketos-ui-plasma-mobile: Remove compile time warning (downloading pre-built packages from the binary repo is working)

* Re-add powerdevil and polkit-kde-agent as runtime deps to postmarketos-ui-plasma-mobile
* Add kwinrc to start applications maximized

It made problems, see #956 and #952. Originally this was added, so
our plasma mobile packaging - which targets wayland - doesn't need
to depend on X11 stuff. And because dbus-x11 caused a 1 minute
wait for an X server (#377).

We have yet to figure out if this problem returns, but even if that
happens, it's better than having it completely broken. And we can
probably figure out a better way to fix it (for real).

* Add postmarketos-ui-plasma-mobile
* Add more required packages
* Upgrade plasma sources
* Modernize APKBUILDs
* Make it run in general
* Support RGB32 framebuffer with BGR order (thanks @zhuowei!)