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/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c

@@ -220,7 +220,7 @@ InitCpuHotEjectData (
       RETURN_ERROR (SafeUintnAdd (Size, sizeof (*mCpuHotEjectData), &Size)) ||
       RETURN_ERROR (SafeUintnAdd (Size, sizeof (UINT64) - 1, &Size)))
   {
-    DEBUG ((DEBUG_ERROR, "%a: invalid CPU_HOT_EJECT_DATA\n", __FUNCTION__));
+    DEBUG ((DEBUG_ERROR, "%a: invalid CPU_HOT_EJECT_DATA\n", __func__));
     goto Fatal;
   }
 
@@ -303,7 +303,7 @@ SmmCpuFeaturesSmmRelocationComplete (
     DEBUG ((
       DEBUG_ERROR,
       "%a: MemEncryptSevSetPageEncMask(): %r\n",
-      __FUNCTION__,
+      __func__,
       Status
       ));
     ASSERT (FALSE);