ARM: integrator: convert PCIv3 bridge to platform device

This converts the PCIv3 driver to a platform device driver, and
registers the device only on the Integrator/AP instead of bailing
out in the initcall if the platform is not correct.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>