sstatesig: add a new info level for SIGGEN_LOCKEDSIGS_TASKSIG_CHECK

sstatesig: add a new info level for SIGGEN_LOCKEDSIGS_TASKSIG_CHECK

as of now, SIGGEN_LOCKEDSIGS_TASKSIG_CHECK can take 2 values: "warn" and
"error", displaying respectively a warning or a fatal error message
only when a task is locked and the task signature is different from
the locked one.

The "info" level is introduced to add a "note" message to remind the
user that a recipe is locked even if the signature is equivalent to the
locked one.

The "warn" and "error" level display the warn/error message for each
task having a mismatch of the signature. Doing this with the "info"
level would result in very verbose output if there are several tasks
locked, so the info level will only print once the list of recipes that
have locked signature.

Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>