sh: mach-highlander and mach-rsk require gpiolib.

Fix up the build for mach-highlander and mach-rsk. These operated on the
assumption that GENERIC_GPIO support with an optional GPIOLIB was
possible. This used to be true, but has not been the case since commit-id
d56cc8bc661ac1ceded8d45ba2d53bb134fee17d ("sh: use gpiolib"), where the
GENERIC_GPIO implementation was rewritten to use GPIOLIB directly.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>