MdePkg: 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: Liming Gao <gaoliming@byosoft.com.cn>

MdePkg/Library/BaseLib/SwitchStack.c

@@ -41,8 +41,8 @@ VOID
 EFIAPI
 SwitchStack (
   IN      SWITCH_STACK_ENTRY_POINT  EntryPoint,
-  IN      VOID                      *Context1,  OPTIONAL
-  IN      VOID                      *Context2,  OPTIONAL
+  IN      VOID                      *Context1   OPTIONAL,
+  IN      VOID                      *Context2   OPTIONAL,
   IN      VOID                      *NewStack,
   ...
   )