MdePkg/UefiLib: move InternalEmptyFunction to UefiLib.c

The InternalEmptyFunction() is currently only used by code in
"UefiNotTiano.c" -- "Library functions that abstract areas of conflict
between framework and UEFI 2.0.". In the next patches,
InternalEmptyFunction() will be used from "UefiLib.c" as well, hence
promote it to "general utility" status: move the function definition to
"UefiLib.c", and place the function declaration (which is already extern)
into "UefiLibInternal.h".

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Library/UefiLib/UefiLib.c

@@ -1545,3 +1545,22 @@ GetBestLanguage (
   return NULL;
 }
 
+/**
+  An empty function to pass error checking of CreateEventEx ().
+
+  This empty function ensures that EVT_NOTIFY_SIGNAL_ALL is error
+  checked correctly since it is now mapped into CreateEventEx() in UEFI 2.0.
+
+  @param  Event                 Event whose notification function is being invoked.
+  @param  Context               The pointer to the notification function's context,
+                                which is implementation-dependent.
+
+**/
+VOID
+EFIAPI
+InternalEmptyFunction (
+  IN EFI_EVENT                Event,
+  IN VOID                     *Context
+  )
+{
+}