MdeModulePkg: Update code to be more C11 compliant by using __func__

__FUNCTION__ is a pre-standard extension that gcc and Visual C++ among
others support, while __func__ was standardized in C99.

Since it's more standard, replace __FUNCTION__ with __func__ throughout
MdeModulePkg.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

MdeModulePkg/Universal/PCD/Dxe/Service.c

@@ -1632,7 +1632,7 @@ GetExPcdTokenNumber (
     }
   }
 
-  DEBUG ((DEBUG_ERROR, "%a: Failed to find PCD with GUID: %g and token number: %d\n", __FUNCTION__, Guid, ExTokenNumber));
+  DEBUG ((DEBUG_ERROR, "%a: Failed to find PCD with GUID: %g and token number: %d\n", __func__, Guid, ExTokenNumber));
   ASSERT (FALSE);
 
   return 0;