microblaze: remove ARCH_WANT_OPTIONAL_GPIOLIB

This symbols is not needed to get access to selecting the
GPIOLIB anymore: any arch can select GPIOLIB.

Cc: Michael Büsch <m@bues.ch>
Cc: Michal Simek <monstr@monstr.eu>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

arch/microblaze/Kconfig

@@ -3,7 +3,6 @@ config MICROBLAZE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_WANT_IPC_PARSE_VERSION
-	select ARCH_WANT_OPTIONAL_GPIOLIB
 	select BUILDTIME_EXTABLE_SORT
 	select CLKSRC_OF
 	select CLONE_BACKWARDS3