MdePkg/BaseLib: Move CHAR_NULL definition to Base.h in BaseLib

- Required unicode control chars -> Null character
- Remove CHAR_NULL definition in SimpleTextIn.h
- https://bugzilla.tianocore.org/show_bug.cgi?id=172

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Bell Song <binx.song@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Include/Base.h

@@ -338,6 +338,11 @@ struct _LIST_ENTRY {
 ///
 #define NULL  ((VOID *) 0)
 
+//
+// Null character
+//
+#define CHAR_NULL             0x0000
+
 ///
 /// Maximum values for common UEFI Data Types
 ///

MdePkg/Include/Protocol/SimpleTextIn.h

@@ -46,7 +46,6 @@ typedef struct {
 //
 // Required unicode control chars
 //
-#define CHAR_NULL             0x0000
 #define CHAR_BACKSPACE        0x0008
 #define CHAR_TAB              0x0009
 #define CHAR_LINEFEED         0x000A