Just noticed that this HP zbook is our last Optimus machine ("Viper"). suspend
works with intel (nouveau driver disabled; nvidia driver installed but
disabled), nouveau(intel gfx disabled in BIOS) and nvidia (intel gfx disabled
in BIOS) drivers on openSUSE Leap 42.1. Indeed it wakes up again immediately
when intel gfx is enabled in BIOS and nouveau driver/kernel module has enabled
the NVIDIA GPU somehow.