There is no need to be stuck with OF node when we may use agnostic
firmware node instead.

It allows users to get property if needed independently of provider.

Note, some OF parts are left because %pfw [1] is in progress.

[1]: https://lore.kernel.org/patchwork/cover/1054863/Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>