drm/sun4i: Enable DW HDMI PHY clock

Current DW HDMI PHY code never prepares and enables PHY clock after it is
created. It's just used as it is. This may work in some cases, but it's
clearly wrong. Fix it by adding proper calls to enable/disable PHY
clock.

Fixes: 4f86e817 ("drm/sun4i: Add support for H3 HDMI PHY variant")

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180625120304.7543-17-jernej.skrabec@siol.net