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/ArmVirtGicArchLib/ArmVirtGicArchLib.c

@@ -150,7 +150,7 @@ ArmVirtGicArchLibConstructor (
       break;
 
     default:
-      DEBUG ((DEBUG_ERROR, "%a: No GIC revision specified!\n", __FUNCTION__));
+      DEBUG ((DEBUG_ERROR, "%a: No GIC revision specified!\n", __func__));
       return RETURN_NOT_FOUND;
   }