i965/skl: Remove early platform support

i965/skl: Remove early platform support

We do not want bug reports from this early stepping of SKL. Few if any were ever
shipped outside of Intel to early enabling partners, and none will be sold.

There is a functional change here. If you're using new mesa on an old
kernel/libdrm, the revid will be -1, and we'll use new SKL values instead of
early ones (a hopefully irrelevant improvement IMO).

v2: Remove hunk which warned before dying. Instead, default to normal SKL
support (Ken)

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Neil Roberts <neil@linux.intel.com>