PEL: switch fmt::format to use std::format

fmt::format is supported in the c++ std. This will
    help to remove fmt package dependency.

Change-Id: I89f0a5b67bbfe54168a20e93c989a1ae87f54503
Signed-off-by: Jayanth Othayoth <ojayanth@in.ibm.com>
diff --git a/extensions/openpower-pels/generic.cpp b/extensions/openpower-pels/generic.cpp
index 0aed07b..52616fa 100644
--- a/extensions/openpower-pels/generic.cpp
+++ b/extensions/openpower-pels/generic.cpp
@@ -15,10 +15,10 @@
  */
 #include "generic.hpp"
 
-#include <fmt/format.h>
-
 #include <phosphor-logging/log.hpp>
 
+#include <format>
+
 namespace openpower
 {
 namespace pels
@@ -57,7 +57,7 @@
     catch (const std::exception& e)
     {
         log<level::ERR>(
-            fmt::format("Cannot unflatten generic section: {}", e.what())
+            std::format("Cannot unflatten generic section: {}", e.what())
                 .c_str());
         _valid = false;
     }