[pvr] fix internal group loading

As we never load the internal groups from our TV database, changing the group name in our group manager has no effect. This fixes the loading of the internal channel groups.
[pvr] cosmetics: refactor internal group id constants to be more meaningful
vaapi: flush ffmpeg buffers if it holds any refs on close
vaapi: drop unused member
renderer: bump number of buffers for vdpau and vaapi
Merge pull request #5391 from FernetMenta/vaapivdpau

Vaapivdpau: fix and optimization
[win32] fix detection of old XBMC install and remove XBMC regkeys
[win32] show message in installer that userdata was moved to new location
Merge pull request #5376 from xhaggi/pvr-fix-internal-group-loading

[pvr] fix internal group loading
Merge remote-tracking branch 'upstream-ro/master'