[dynui] Add concept of a secret user interface item

For interactive forms, the concept of a secret value becomes
meaningful (e.g. for password fields).

Add a flag to indicate that an item represents a secret value, and
allow this flag to be set via the "--secret" option of the "item"
command.

This flag has no meaning for menu items, but is silently accepted
anyway to keep the code size minimal.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/dynui.h

@@ -44,6 +44,9 @@ struct dynamic_item {
 /** Dynamic user interface item is default selection */
 #define DYNUI_DEFAULT 0x0001
 
+/** Dynamic user interface item represents a secret */
+#define DYNUI_SECRET 0x0002
+
 extern struct dynamic_ui * create_dynui ( const char *name, const char *title );
 extern struct dynamic_item * add_dynui_item ( struct dynamic_ui *dynui,
 					      const char *name,