drm/exynos: Don't reset hdmiphy on hdmi off

This patch removes the hdmiphy reset in hdmi_poweroff. The hdmiphy reset
was added to take advantage of exynos clockgating, doing it would gate
the entire TV domain. Unfortunately, mixer is included in the TV domain
and its vsync interrupts are stopped when TV is gated.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rahul Sharma <Rahul.Sharma@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>