drm/msm: fence wait-boost support

If the guest tells us that it is waiting for a fence, and the host kernel is new enough, trigger wait-boost. This is useful for games like Genshin Impact which (presumably inadvertently) wait every frame on a just-rendered FBO (it does seem to triple buffer that FBO, making me think it is trying to readpix from the wrong buffer), which results in stalls that cause host gpu devfreq to ramp down the freq.