ARM: dts: Use GPIO constants for flags cells in exynos5420/5422/5800 boards

The board DTS are using numeric values instead of the defined GPIO
constanst to express polarity, use them to make the DTS more clear.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>