blackfin: do away with ARCH_REQUIRE_GPIOLIB

Replace "select ARCH_REQUIRE_GPIOLIB" with "select GPIOLIB"
as this can now be selected directly.

Cc: Michael Büsch <m@bues.ch>
Cc: Steven Miao <realmz6@gmail.com>
Cc: adi-buildroot-devel@lists.sourceforge.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>