SecurityPkg/RngDxe: Add debug warning for NULL PcdCpuRngSupportedAlgorithm

PcdCpuRngSupportedAlgorithm should allow to identify the the algorithm
used by the RNDR CPU instruction to generate a random number.
Add a debug warning if the Pcd is not set.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Acked-by: Jiewen Yao <jiewen.yao@intel.com>

SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/RngDxe.c

@@ -67,6 +67,16 @@ GetAvailableAlgorithms (
       sizeof (EFI_RNG_ALGORITHM)
       );
     mAvailableAlgoArrayCount++;
+
+    DEBUG_CODE_BEGIN ();
+    if (IsZeroGuid (PcdGetPtr (PcdCpuRngSupportedAlgorithm))) {
+      DEBUG ((
+        DEBUG_WARN,
+        "PcdCpuRngSupportedAlgorithm should be a non-zero GUID\n"
+        ));
+    }
+
+    DEBUG_CODE_END ();
   }
 
   // Raw algorithm (Trng)