MdeModulePkg: 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
MdeModulePkg.

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>

MdeModulePkg/Bus/Pci/XhciDxe/Xhci.c

@@ -2059,7 +2059,7 @@ XhcDriverBindingStart (
       DEBUG ((
         DEBUG_WARN,
         "%a: failed to enable 64-bit DMA on 64-bit capable controller @ %p (%r)\n",
-        __FUNCTION__,
+        __func__,
         Controller,
         Status
         ));