lora: Use generic node name "lora" for all lora nodes

The current devicetree specification (master branch [1]) lists "lora" as
a generic node name. Hence, all devicetree files in Zephyr should use
the same.

[1] https://github.com/devicetree-org/devicetree-specification/blob/main/source/chapter2-devicetree-basics.rst



Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>