Add missing format conversions for SPA_VIDEO_FORMAT_{xBGR,ABGR}

These enum values are already handled in createFormatsParams and
pwhelpers.cpp, just not here.

This also removes duplicates of these values from createFormatsParams.

For me, this change fixes thumbnail display in Plasma's TM:

    kpipewire_logging: cannot convert spa format to fourcc {10,14}
    kpipewire_logging: Stream error:  no more input formats
    kpipewire_logging: PipeWire remote error:  -32 no more input formats

— although they are still vertically flipped
(existing bug report: https://bugs.kde.org/show_bug.cgi?id=479083).

BUG: 478309