demmt/nvrm: add NVRM_PARAM_SUBDEVICE_BUS_EXP_LNK_CAP
demmt/nvrm: IOCTL_UNK48 deals with PDISPLAY

In nv92 modesetting traces it touches registers from
PDISPLAY.VGA.* range.
demmt/nvrm: s/IOCTL_UNK41/IOCTL_SCHED_FIFO/

It pauses PFIFO, puts one channel on a playlist, resumes PFIFO,
pauses it again, puts all channels back on a playlist and resumes
PFIFO.

This ioctl is used only in modesetting traces.