ARM: dts: Add node for touchscreen voltage regulator for exynos4210-trats

This patch adds device tree node for a fixed voltage regulator used for
touchscreen on Samsung Trats board.

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