Some units have to be able to set it's own clock precisely to work
correctly. Allow them to do so by adding CLK_SET_RATE_PARENT flag.

Add this flag to DE, TCON and HDMI clocks.
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>