clk: versal: Update the reference clocks as per bindings

clk: versal: Update the reference clocks as per bindings

As per the bindings the reference clocks naming has changed
from "pl_alt_ref_clk" to "pl_alt_ref" and "ref_clk" to "ref".
Update the same in the clock driver. Also add the fallback option
for older DT bindings.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://lore.kernel.org/r/20250206091533.1447234-1-venkatesh.abbarapu@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>