The two GPIO controllers are always mapped to the same virtual address
across all MSM devices.  Instead of selecting this at compile time,
determine the physical address at runtime, eliminating yet something
else preventing multiple MSM targets from being compiled into the same
kernel.

Change-Id: I1672219d978ab6243526adeda6badf49472baa27
Signed-off-by: David Brown <davidb@codeaurora.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>