default the bit per color(bpc) to 8 for better compatibility and user experience
According to the drm/intel#1890 and LP: #1890772 No signal on 4K 60Hz DisplayPort monitor by default, until "max bpc" is lowered to 8, we know ANY component on the pipeline between host to monitor(e.g. socket, converter, dongle, cable, monitor) could impact the compatibility on video/audio transferring bandwidth.
Before the proposal(https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/1108) be accepted, all users just get dark screen or audio lost if any poor component on the pipeline between host to monitor.
Even after the proposal, it's still a poor experience that user encounter a dark screen or function lost on external monitor then need to adjust "max bpc" to get the screen lighted.(user might even not aware adjusting max bpc can fix it.)
So, I propose to default set max bpc to 8 which also the same behavior of what Windows is doing.
The first proposal is to add one more script under /etc/X11/Xsession.d by package x11-common.
This is what I tried for LP: #1890772 No signal on 4K 60Hz DisplayPort monitor by default, until "max bpc" is lowered to 8