The CPUX clock on A33, which is for the Cortex-A7 cores, is designed to
be changeable by changing the rate of PLL_CPUX.

Add CLK_SET_RATE_PARENT flag to this clock.
Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>