gpio: ich: Add support for Intel Avoton

This patch adds support for Atom C2000 series (Avoton and Rangeley). And has
the following options:
  - New addresses register.
  - Caching output levels (see Intel external design spec, table 48-29)
  - No hardware blink.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vincent Donnefort <vdonnefort@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>