dt-bindings: memory: lpddr2: Add revision-id properties

Add optional revision-id standard LPDDR2 properties which will help to
identify memory chip.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211006224659.21434-4-digetx@gmail.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>