clk: sunxi-ng: h3: gate then ungate PLL CPU clk after rate change

This patch utilizes the new PLL clk notifier to gate then ungate the
PLL CPU clock after rate changes. This should prevent any system hangs
resulting from cpufreq changes to the clk.

Reported-by: Ondrej Jirman <megous@megous.com>
Fixes: 0577e485 ("clk: sunxi-ng: Add H3 clocks")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Tested-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>