dt-bindings: sram: Add compatible for ST-Ericsson U8500 eSRAM

This adds an SoC-specific binding for the banks of eSRAM
available in the ST-Ericsson U8500.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230417-ux500-sram-v2-1-6e62ad551faa@linaro.org