Disable bulk fetch. Add environment variable to enable it

RDC can optimize by bulk fetching multiple metrics using a single
rocm_smi call. However, currently this is not completely supported in
all ASIC generations. By default disable this for now.

Set environment variable RDC_BULK_FETCH_ENABLED=TRUE to enable
RDC bulk fetch.

BUG: SWDEV-289316

Change-Id: Ibb55514f198356dccf5f47bb0fd2d53c17acb251

include/rdc_lib/impl/RdcSmiLib.h

@@ -70,6 +70,7 @@ class RdcSmiLib : public RdcTelemetry, public RdcDiagnostic {
 
  private:
     RdcMetricFetcherPtr metric_fetcher_;
+    bool bulk_fetch_enabled_;
 };
 
 typedef std::shared_ptr<RdcSmiLib> RdcSmiLibPtr;