UefiCpuPkg: 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
UefiCpuPkg.

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: Ray Ni <ray.ni@intel.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>

UefiCpuPkg/Library/MpInitLib/PeiMpLib.c

@@ -758,7 +758,7 @@ PlatformShadowMicrocode (
   DEBUG ((
     DEBUG_INFO,
     "%a: Required microcode patches have been loaded at 0x%lx, with size 0x%lx.\n",
-    __FUNCTION__,
+    __func__,
     CpuMpData->MicrocodePatchAddress,
     CpuMpData->MicrocodePatchRegionSize
     ));