envfs: provide an intentional way to ignore an existing external environment
Add a simple flag to envfs to be able to mark an external environment as
"not to be used".
This change should not affect existing systems, because the current envfs
implementation ensures the 'flags' member in the envfs master block is always
zeroed.
Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>