ARM: dts: add PCI to the Gemini device trees

The Cortina Gemini has an internal PCI root bus, add this to
the device tree, and add interrupt mapping (swizzling) to the
relevant systems device trees.

Cc: Janos Laube <janos.dev@gmail.com>
Cc: Paulius Zaleckas <paulius.zaleckas@gmail.com>
Cc: Hans Ulli Kroll <ulli.kroll@googlemail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Feng-Hsin Chiang <john453@faraday-tech.com>
Cc: Greentime Hu <green.hu@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>