ARM: dts: Add device nodes for GScaler blocks for exynos5420

Adds G-Scaler device nodes to the DT device list

Signed-off-by: Leela Krishna Amudala <l.krishna@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>