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/CpuS3DataDxe/CpuS3Data.c

@@ -127,7 +127,7 @@ CpuS3DataOnEndOfDxe (
                                                     );
   ASSERT_EFI_ERROR (Status);
 
-  DEBUG ((DEBUG_VERBOSE, "%a\n", __FUNCTION__));
+  DEBUG ((DEBUG_VERBOSE, "%a\n", __func__));
   MtrrGetAllMtrrs (&AcpiCpuDataEx->MtrrTable);
 
   //