dt-bindings: sram: qcom,imem: Narrow allowed reboot modes

Only few Qualcomm IMEM devices actually provide interface for setting
reboot modes, but top-level schema allows "reboot-mode" child for
everyone.  Narrow this to specific compatibles.

syscon-reboot-mode schema allows arbitrary "mode-.* properties but only
a subset actually makes sense and is valid.  Provide negative look-ahead
pattern to disallow any modes not supported by the device, which
tightens the binding even more.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260701105832.197036-2-krzysztof.kozlowski@oss.qualcomm.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/sram/qcom,imem.yaml

@@ -89,6 +89,26 @@ required:
   - compatible
   - reg
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - qcom,apq8064-imem
+              - qcom,msm8226-imem
+              - qcom,msm8974-imem
+    then:
+      properties:
+        reboot-mode:
+          patternProperties:
+            # Negative look-ahead to disallow unsupported modes. The '$' has to be
+            # part of lookahead group to work, instead of trailing outside of ().
+            "^mode-(?!(bootloader$|normal$|recovery$))": false
+    else:
+      properties:
+        reboot-mode: false
+
 additionalProperties: false
 
 examples: