arm: configs: spear6xx: Refresh defconfig

Refresh the defconfig to follow the changes made over the year.
I ensure important options have not gone away.
I drop the gpio sysfs config as it is useless to keep it alone without
CONFIG_EXPERT.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>