dt-bindings: memory: Add jedec,lpddrX-channel binding

dt-bindings: memory: Add jedec,lpddrX-channel binding

This patch adds a new device tree binding for an LPDDR channel to serve
as a top-level organizing node for LPDDR part nodes nested below it. An
LPDDR channel needs to have an "io-width" property to describe its width
(this is important because this width does not always match the io-width
of the part number, indicating that multiple parts are wired in parallel
on the same channel), as well as one or more nested "rank@X" nodes.
Those represent information about the individual ranks of each LPDDR
part connected on that channel and should match the existing
"jedec,lpddrX" bindings for individual LPDDR parts.

New platforms should be using this node -- the existing practice of
providing a raw, toplevel "jedec,lpddrX" node without indication of how
many identical parts are in the system should be considered deprecated.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220930220606.303395-4-jwerner@chromium.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>