dri: Merge drisw_util.c into dri_util.c

dri: Merge drisw_util.c into dri_util.c

The only important difference was not calling drmGetVersion, and making
the swrast extension vtable.  That doesn't justify duplicating the other
330 lines of code.

v2: fix the scons build (code by Emil Velikov)
v3: fix scons build with swrast-only (code by Emil Velikov)
v4: Drop the new define I added, when we already have __NOT_HAVE_DRM_H.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>