drm: sun4i: drop second PLL from A64 HDMI PHY

The A64 HDMI PHY seems to be not able to use the second video PLL as
clock parent in experiments.

Drop the support for the second PLL from A64 HDMI PHY driver.

Fixes: b46e2c9f

 ("drm/sun4i: Add support for A64 HDMI PHY")
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180916043409.62374-2-icenowy@aosc.io