[NTOS:MM] Allow contiguous-memory frees at DISPATCH_LEVEL (#9349)

MmFreeContiguousMemory() is callable at up to DISPATCH_LEVEL,
but MiFreeContiguousMemory() used PAGED_CODE(), which incorrectly asserted
above APC_LEVEL in checked builds.

Replace it with an assertion that enforces the exported IRQL contract.

ntoskrnl/mm/ARM3/contmem.c

@@ -464,7 +464,7 @@ MiFreeContiguousMemory(IN PVOID BaseAddress)
     PFN_NUMBER PageFrameIndex, LastPage, PageCount;
     PMMPFN Pfn1, StartPfn;
     PMMPTE PointerPte;
-    PAGED_CODE();
+    ASSERT_IRQL_LESS_OR_EQUAL(DISPATCH_LEVEL);
 
     //
     // First, check if the memory came from initial nonpaged pool, or expansion