of/address: Add of_range_count() helper

Some users need a count of the number of ranges entries before
iterating over the entries. Typically this is for allocating some data
structure based on the size. Add a helper, of_range_count(), to get the
count. The helper must be called with an struct of_range_parser
initialized by of_range_parser_init().

Link: https://lore.kernel.org/r/20230328-dt-address-helpers-v1-4-e2456c3e77ab@kernel.org


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