clk: sunxi: display: Add per-clock flags

The TCON channel 0 clock that is the parent clock of our pixel clock is
expected to change its rate depending on the resolution we want to output
in our display engine.

However, since it's only a mux, the only way it can do that is by changing
its parents rate.

Allow to give flags in our display clocks description, and add the
CLK_SET_RATE_PARENT flag for the TCON channel 0 flag.

Fixes: a3b4956ee6d9 ("clk: sunxi: display: Add per-clock flags")
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>