spi: dt-bindings: Describe stacked/parallel memories modes

Describe two new memories modes:
- A stacked mode when the bus is common but the address space extended
  with an additinals wires.
- A parallel mode with parallel busses accessing parallel flashes where
  the data is spread.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220126112608.955728-3-miquel.raynal@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml

@@ -82,6 +82,31 @@ properties:
     description:
       Delay, in microseconds, after a write transfer.
 
+  stacked-memories:
+    description: Several SPI memories can be wired in stacked mode.
+      This basically means that either a device features several chip
+      selects, or that different devices must be seen as a single
+      bigger chip. This basically doubles (or more) the total address
+      space with only a single additional wire, while still needing
+      to repeat the commands when crossing a chip boundary. The size of
+      each chip should be provided as members of the array.
+    $ref: /schemas/types.yaml#/definitions/uint64-array
+    minItems: 2
+    maxItems: 4
+
+  parallel-memories:
+    description: Several SPI memories can be wired in parallel mode.
+      The devices are physically on a different buses but will always
+      act synchronously as each data word is spread across the
+      different memories (eg. even bits are stored in one memory, odd
+      bits in the other). This basically doubles the address space and
+      the throughput while greatly complexifying the wiring because as
+      many busses as devices must be wired. The size of each chip should
+      be provided as members of the array.
+    $ref: /schemas/types.yaml#/definitions/uint64-array
+    minItems: 2
+    maxItems: 4
+
 # The controller specific properties go here.
 allOf:
   - $ref: cdns,qspi-nor-peripheral-props.yaml#