st/dri: Reshuffle files and make it obvious which files are shared

In short:
git mv ../drisw/Makefile dri/sw
git mv drisw.[c|h] sw
git mv dri2.[c|h] dri1.[c|h] Makefile drm
git rm ../drisw
ln -s <common files> drm/*
ln -s <common files> sw/*
37 files changed