soc: xilinx: vcu: register PLL as fixed rate clock

soc: xilinx: vcu: register PLL as fixed rate clock

Currently, xvcu_pll_set_rate configures the PLL to a clock rate that is
pre-calculated when probing the driver. To still make the clock
framework aware of the PLL and to allow to configure other clocks based
on the PLL rate, register the PLL as a fixed rate clock.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/20210121071659.1226489-8-m.tretter@pengutronix.de
Signed-off-by: Stephen Boyd <sboyd@kernel.org>