property: Add functions to iterate named child

There are a few use-cases where child nodes with a specific name need to
be parsed. Code like:

fwnode_for_each_child_node()
	if (fwnode_name_eq())
		...

can be found from a various drivers/subsystems. Adding a macro for this
can simplify things a bit.

In a few cases the data from the found nodes is later added to an array,
which is allocated based on the number of found nodes. One example of
such use is the IIO subsystem's ADC channel nodes, where the relevant
nodes are named as channel[@N].

Add helpers for iterating and counting device's sub-nodes with certain
name instead of open-coding this in every user.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Link: https://patch.msgid.link/2767173b7b18e974c0bac244688214bd3863ff06.1742560649.git.mazziesaccount@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>