ARM64: Make ARCH_NR_GPIO a Kconfig variable

Have ARCH_NR_GPIO configurable in ARM64 similar to how it
is in ARM.

Change-Id: I7b292a9f2cb8925382a6478a52e85f831ddbc123
Signed-off-by: Kyle Yan <kyan@codeaurora.org>
Signed-off-by: Venkata Narendra Kumar Gutta <vnkgutta@codeaurora.org>