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/extended_user_header.cpp b/extensions/openpower-pels/extended_user_header.cpp
index 4f54518..1867673 100644
--- a/extensions/openpower-pels/extended_user_header.cpp
+++ b/extensions/openpower-pels/extended_user_header.cpp
@@ -19,10 +19,10 @@
 #include "pel_types.hpp"
 #include "pel_values.hpp"
 
-#include <fmt/format.h>
-
 #include <phosphor-logging/log.hpp>
 
+#include <format>
+
 namespace openpower
 {
 namespace pels
@@ -43,7 +43,7 @@
     catch (const std::exception& e)
     {
         log<level::ERR>(
-            fmt::format("Cannot unflatten extended user header: {}", e.what())
+            std::format("Cannot unflatten extended user header: {}", e.what())
                 .c_str());
         _valid = false;
     }
@@ -111,7 +111,7 @@
     if (header().id != static_cast<uint16_t>(SectionID::extendedUserHeader))
     {
         log<level::ERR>(
-            fmt::format("Invalid ExtendedUserHeader section ID: {0:#x}",
+            std::format("Invalid ExtendedUserHeader section ID: {0:#x}",
                         header().id)
                 .c_str());
         failed = true;
@@ -120,7 +120,7 @@
     if (header().version != extendedUserHeaderVersion)
     {
         log<level::ERR>(
-            fmt::format("Invalid ExtendedUserHeader version: {0:#x}",
+            std::format("Invalid ExtendedUserHeader version: {0:#x}",
                         header().version)
                 .c_str());
         failed = true;