OvmfPkg: 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
OvmfPkg.

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>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>

OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c

@@ -294,7 +294,7 @@ IterateVariablesCallbackSetSystemVariable (
       DEBUG_WARN,
       "%a: setting authenticated variable \"%s\" "
       "failed with EFI_SECURITY_VIOLATION, ignoring\n",
-      __FUNCTION__,
+      __func__,
       VariableName
       ));
     Status = EFI_SUCCESS;
@@ -303,7 +303,7 @@ IterateVariablesCallbackSetSystemVariable (
       DEBUG_WARN,
       "%a: setting ReadOnly variable \"%s\" "
       "failed with EFI_WRITE_PROTECTED, ignoring\n",
-      __FUNCTION__,
+      __func__,
       VariableName
       ));
     Status = EFI_SUCCESS;