gpio: mb86s7x: share with other SoCs as module

gpio: mb86s7x: share with other SoCs as module

In order to reuse this driver for the Socionext Synquacer SC2A11 SoC,
which inherited this IP from Fujitsu, remove the ARCH_MB86S7X Kconfig
dependency, and revert the changes that prevent it from being built as
a module.

This reverts commits d65aa4b67b4f47f303bdeaef1e4d42ef18e6b293 and
d5610e514e92144d19bd5e39e5cf3804bbf85f3e.

Cc: Geliang Tang <geliangtang@gmail.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[Folded in module_platform_driver() fixup]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>