Video related clocks need to set rate as close as possible to the
requested one, so they should be able to change parent clock rate.

When processing 4K video, VPU clock has to be set to higher rate than it
is default parent rate. Because of that, VPU clock should be able to
change parent clock rate.

Add CLK_SET_RATE_PARENT flag to tcon-lcd0, tcon-tv0 and ve.
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>