direct3d11: adjust the output luminance to the screen

If we output 100 nits on a sceen that reports 400 nits in SDR mode the picture
will look too dim.

The 270 value is the normal value reported on an SDR screen, so we scale the
screen value accordingly.

Fixes 26112
11 jobs for !652 with d3d11-sdr-peak-luminance in 23 minutes and 18 seconds (queued for 11 seconds)
latest merge request