EmbeddedPkg: Change OPTIONAL keyword usage style

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3760

Update all use of ', OPTIONAL' to ' OPTIONAL,' for function params.

Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael Kubacki <michael.kubacki@microsoft.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Andrew Fish <afish@apple.com>

EmbeddedPkg/Include/Library/PrePiLib.h

@@ -745,7 +745,7 @@ LoadDxeCoreFromFfsFile (
 EFI_STATUS
 EFIAPI
 LoadDxeCoreFromFv (
-  IN UINTN  *FvInstance,   OPTIONAL
+  IN UINTN  *FvInstance    OPTIONAL,
   IN UINTN  StackSize
   );