Implement BlGetMappingsCount() routine

xtldr/includes/xtldr.h

@@ -135,6 +135,11 @@ EFI_STATUS
 BlGetEfiPath(IN PWCHAR SystemPath,
              OUT PWCHAR *EfiPath);
 
+XTCDECL
+VOID
+BlGetMappingsCount(IN PXTBL_PAGE_MAPPING PageMap,
+                   OUT PULONG NumberOfMappings);
+
 XTCDECL
 EFI_STATUS
 BlGetMemoryMap(OUT PEFI_MEMORY_MAP MemoryMap);