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/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c

@@ -113,7 +113,7 @@ PvalidateRange (
         DEBUG_ERROR,
         "%a:%a: Failed to %a address 0x%Lx Error code %d\n",
         gEfiCallerBaseName,
-        __FUNCTION__,
+        __func__,
         Validate ? "Validate" : "Invalidate",
         Address,
         Ret
@@ -237,7 +237,7 @@ InternalSetPageState (
     DEBUG_VERBOSE,
     "%a:%a Address 0x%Lx - 0x%Lx State = %a LargeEntry = %d\n",
     gEfiCallerBaseName,
-    __FUNCTION__,
+    __func__,
     BaseAddress,
     EndAddress,
     State == SevSnpPageShared ? "Shared" : "Private",