dt-bindings: mfd: Add Delta TN48M CPLD drivers bindings

Add binding documents for the Delta TN48M CPLD drivers.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Link: https://lore.kernel.org/r/20220131133049.77780-6-robert.marko@sartura.hr


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>