ARM: integrator: let pciv3 use mem/premem from device tree

Instead of relying on the hard-coded mem/premem bases for
the PCI side, read in these from the device tree in the
DT probe path. Hard-code the old values on the non-DT probe
path. Introduce some static locals to hold these addresses
instead of the earlier static #defines.

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