arm64: zynqmp: Add clk bindings for RC21008A clock generator

commit 0e9ac750eb93fc52a3535354a28d599237f1fbe7 from
https://github.com/Xilinx/linux-xlnx.git

 xlnx_rebase_v5.15

Add RC21008A clock nodes and fclk bindings so GT clocks could be referenced
through sysfs interface.

Signed-off-by: Saeed Nowshadi <saeed.nowshadi@xilinx.com>
State: pending
Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>