drm/rockchip: dw_hdmi: Move HDMI vpll clock enable to bind()

The HDMI vpll clock should be enabled when bind() is called. So move the
clk_prepare_enable of that clock to bind() function and add the missing
clk_disable_unprepare() required in error handling path and unbind().

Fixes: 12b9f204 ("drm: bridge/dw_hdmi: add rockchip rk3288 support")
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20180302175757.28192-5-enric.balletbo@collabora.com