clk: Ensure the parent clocks are enabled while reparenting

Reparenting a clock C with a new parent P means that C will only
continue clocking if P is already clocking when the mux is updated. In
case the parent is currently disabled, failures (stalls) are likely to
happen.

This is exactly what happens on i.MX8 when enabling the video
pipeline. We tell LCDIF clocks to use the VIDEO PLL as input, while the
VIDEO PLL is currently off. This all happens as part of the
assigned-clocks handling procedure, where the reparenting happens before
the enable() calls. Enabling the parents as part of the reparenting
procedure seems sane and also matches the logic applied in other parts
of the CCM.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

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