drm/exynos: remove hardware overlays disable from fimd probe

System hangs when FIMD registers are accessed to disable
hardware overlays. This is because of the clocks which are
not enabled before register access.

'Hardware overlay disable' is cleaned from the FIMD probe.

Signed-off-by: Rahul Sharma <rahul.sharma@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>