gpio: samsung: Remove legacy support of S5PV210

GPIO support of S5PV210 SoC is now fully handled by pinctrl-samsung
driver making the old code in gpio-samsung driver unused. This patch
removes it which will also let us remove more code from arch subtree.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>