libdpkg: Add new DPKG_BIT macro

lib/dpkg/macros.h

@@ -88,6 +88,13 @@
 #define DPKG_END_DECLS
 #endif
 
+/**
+ * @def DPKG_BIT
+ *
+ * Return the integer value of bit n.
+ */
+#define DPKG_BIT(n)	(1UL << (n))
+
 /**
  * @def array_count
  *