nvmem: Change to unified property interface Change from using device tree (Open Firmware) APIs to the unified 'fwnode' interface. Change of_nvmem_cell_get() to fwnode_nvmem_cell_get(), and add a wrapper for of_nvmem_cell_get(). Change of_nvmem_device_get() to fwnode_nvmem_device_get(). There are no known accessors to the OF interface, so no need for a wrapper. The first version of this patch incorrectly had a wrapper for of_nvmem_device_get(), even though the comments about the patch not needing this were correct. The second version of this patch had an incorrect return type for of_nvmem_device_get().
