[Silabs] Move NVM semaphore creation to nvm3_lockBegin() (#26270)

* Move NVM initialization to sl_platform_init() in matter_support submodule

Also move nvm3_Sem creation to nvm3_lockBegin()

* Restore the call to nvm3_open(), it's safe to call multiple times

src/platform/silabs/SilabsConfig.cpp

@@ -43,6 +43,12 @@ static StaticSemaphore_t nvm3_SemStruct;
 
 void nvm3_lockBegin(void)
 {
+    if (nvm3_Sem == NULL)
+    {
+        nvm3_Sem = xSemaphoreCreateBinaryStatic(&nvm3_SemStruct);
+        xSemaphoreGive(nvm3_Sem);
+    }
+
     VerifyOrDie(nvm3_Sem != NULL);
     xSemaphoreTake(nvm3_Sem, portMAX_DELAY);
 }
@@ -65,15 +71,8 @@ namespace Internal {
 
 CHIP_ERROR SilabsConfig::Init()
 {
-#ifndef BRD4325A // TODO: fix semaphore usage in nvm3_lock for siwx917. use weak implementation for that board instead
-    nvm3_Sem = xSemaphoreCreateBinaryStatic(&nvm3_SemStruct);
+    // nvm3_Sem is created in nvm3_lockBegin()
 
-    if (nvm3_Sem == NULL)
-    {
-        return CHIP_ERROR_NO_MEMORY;
-    }
-    xSemaphoreGive(nvm3_Sem);
-#endif // not BRD4325A
     return MapNvm3Error(nvm3_open(nvm3_defaultHandle, nvm3_defaultInit));
 }