soc: xilinx: vcu: make the PLL configurable

soc: xilinx: vcu: make the PLL configurable

Do not configure the PLL when probing the driver, but register the clock
in the clock framework and do the configuration based on the respective
callbacks.

This is necessary to allow the consumers, i.e., encoder and decoder
drivers, of the xlnx_vcu clock provider to set the clock rate and
actually enable the clocks without relying on some pre-configuration.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/20210121071659.1226489-11-m.tretter@pengutronix.de
Signed-off-by: Stephen Boyd <sboyd@kernel.org>