ARM: dts: fix lid and power pin-functions for exynos5250-spring

Configure the pins in external interrupt mode, as done for Snow in
e5e5c6d1

 ("ARM: dts: Add power and lid GPIO keys pinctrl for
exynos5250-snow").

Reported-by: Kukjin Kim <kgene@kernel.org>
Suggested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Fixes: 53dd4138

 ("ARM: dts: Add exynos5250-spring device tree")
Signed-off-by: Andreas Faerber <afaerber@suse.de>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Kukjin Kim <kgene@kernel.org>