dt-bindings: memory: lpddr2: Convert to schema

Convert LPDDR2 binding to schema. I removed obsolete ti,jedec-lpddr2-*
compatibles since they were never used by device-trees and by the code.
I also changed "Elpida" compatible prefix to lowercase "elpida".

Suggested-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211006224659.21434-3-digetx@gmail.com


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