dt-bindings: sram: qcom,imem: add IMEM memory region

Add bindings for IMEM memory region (like SRAM) used on several
Qualcomm SoCs.  In the downstream (vendor) tree, it comes with several
children used for debugging purposes.  The upstreamed parts are much
smaller - just image loader and syscon reboot.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220607171848.535128-2-krzysztof.kozlowski@linaro.org