clk: exynos5250: register display block gate clocks to common clock framework

Add gate clocks for fimd, mie, dsim, dp, mixer and hdmi.
Register it to common clock framework.

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