clk: zte: set CLK_SET_RATE_PARENT for a few zx296718 clocks

To support VOU VGA display driver with different modes, we need to set
flag for a few clocks, so that clk_set_rate() call in VOU driver can get
VGA device desired pixel rate.

While at it, the divider between pll_vga and clk_vga gets corrected, as
it's 1:1 instead of 1:2.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>