drm/exynos: replace hdmi reset with hdmi disable

Before setting the core and timing generation registers,
hdmi driver resets the whole hdmi hardware, which also
resets the audio related registers.

Hdmi reset is replaced by hdmi disable which is called
just before setting the core and timing registers. It
also ensure that audio settings are not changed.

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