clk: sunxi-ng: fix PLL_CPUX adjusting on A33

[ Upstream commit 790d929b ]

When adjusting PLL_CPUX on A33, the PLL is temporarily driven too high,
and the system hangs.

Add a notifier to avoid this situation by temporarily switching to a
known stable 24 MHz oscillator.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>