ARM: dts: Add utility macro to define pin sleep states for exynos4x12-pinctrl

This patch adds a convenient macro which constructs an Exynos pinctrl
pinconf node containing properties needed to configure sleep state of
given pin with given parameters. It will be used by further patch which
adds a large number of sleep states for pins that need such
configuration on certain boards.

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