drm/exynos: support device tree for fimd

This adds the of_match_table to exynos-drm fimd driver to be probed from
the device tree.

Changelog v2:
- fix build error without CONFIG_OF.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>