ArmVirtPkg: 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
ArmVirtPkg.

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>

ArmVirtPkg/Library/KvmtoolRtcFdtClientLib/KvmtoolRtcFdtClientLib.c

@@ -147,7 +147,7 @@ KvmtoolRtcFdtClientLibConstructor (
     DEBUG ((
       DEBUG_ERROR,
       "%a: No 'motorola,mc146818' compatible DT node found\n",
-      __FUNCTION__
+      __func__
       ));
     return Status;
   }
@@ -163,7 +163,7 @@ KvmtoolRtcFdtClientLibConstructor (
     DEBUG ((
       DEBUG_ERROR,
       "%a: No 'reg' property found in 'motorola,mc146818' compatible DT node\n",
-      __FUNCTION__
+      __func__
       ));
     return Status;
   }