video: exynos_dp: Add device tree support to DP driver

This patch enables device tree based discovery support for DP driver.
The driver is modified to handle platform data in both the cases:
with DT and non-DT.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>