dt-bindings: power: xilinx: merge zynqmp-genpd.txt with firmware binding

Remove the zynqmp-genpd.txt binding. Add the power-domain-cells
property from the zynqmp-genpd.txt binding to firmware binding.

Signed-off-by: Naman Trivedi Manojbhai <naman.trivedimanojbhai@amd.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230816130309.1338446-1-naman.trivedimanojbhai@amd.com


Signed-off-by: Rob Herring <robh@kernel.org>