spi: Stacked/parallel memories bindings

Merge series from Miquel Raynal <miquel.raynal@bootlin.com>:

DT bindings for stacked and parallel flash/memory devices.

base-commit: 991a5e519c2aa1f4ed2bf6e2139997d7e7967cb3

diff --cc Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
Simple merge