soc: xilinx: vcu: implement clock provider for output clocks

soc: xilinx: vcu: implement clock provider for output clocks

The VCU System-Level Control uses an internal PLL to drive the core and
MCU clock for the allegro encoder and decoder based on an external PL
clock.

In order be able to ensure that the clocks are enabled and to get their
rate from other drivers, the module must implement a clock provider and
register the clocks at the common clock framework. Other drivers are
then able to access the clock via devicetree bindings.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/20210121071659.1226489-9-m.tretter@pengutronix.de
Signed-off-by: Stephen Boyd <sboyd@kernel.org>