ARM: SAMSUNG: Remove useless Samsung GPIO related CONFIG

The Kconfig entry for S3C_GPIO_CFG_S3C64XX was missed by commit
5ec74144 ("ARM: SAMSUNG: Remove useless Samsung GPIO related
CONFIGs"). Remove it now.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>