Add support for Intel Silvermont: Bay Trail, Rangeley and Avoton.

The core of this patch to support Bay Trail originally came from the
Chromiumos flashrom repo and was modified by Sage to support the
Rangeley/Avoton parts as well.
Because that was not complicated enough already Stefan Tauner refactored
and refined everything. Bay Trail seems to be the first Atom SoC able to
support hwseq. No SPI Programming Guide could be obtained so it is
handled similarly to Lynx Point which seems to be its nearest relative.

Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Signed-off-by: Martin Roth <gaumless@gmail.com>
Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Add support for Intel Wildcat Point PCH.

The Wildcat Point PCH can be paired with Broadwell or Haswell.
This patch was essentially backported from ChromiumOS commit 9bd2af8.

Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>