login: XGI Z7/Z9 (XG20 core) graphic chip requires master-of-seat to be set

This graphic chip doesn't have a DRM driver and fall back to vesa-framebuffer
driver.

Without this patch, users of such chip suddenly see their GUI broken without
any indication or reason of what happened (no error message). Hence this
regression is near to impossible to troubleshoot for end users. Such case was
reported https://bugzilla.opensuse.org/show_bug.cgi?id=1187154.

Rather than adding another exception in the udev rules to deal with such
HWs, they instead get their own hwdb file '60-seat.hwdb'.