Changesets are very powerful, but the lack of a helper API
makes using them cumbersome. Introduce a simple copy based
API that makes things considerably easier.

To wit, adding a property using the raw API.

	struct property *prop;
	prop = kzalloc(sizeof(*prop)), GFP_KERNEL);
	prop->name = kstrdup("compatible");
	prop->value = kstrdup("foo,bar");
	prop->length = strlen(prop->value) + 1;
	of_changeset_add_property(ocs, np, prop);

while using the helper API

	of_changeset_add_property_string(ocs, np, "compatible",
			"foo,bar");

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>