NOR: invalidate cached state on target resume

The NOR infrastructure caches some per-sector state, but
it's not used much ... because the cache is not trustworthy.

This patch addresses one part of that problem, by ensuring
that state cached by NOR drivers gets invalidated once we
resume the target -- since targets may then modify sectors.

Now if we see sector protection or erase status marked as
anything other than "unknown", we should be able to rely
on that as being accurate.  (That is ... if we assume the
drivers initialize and update this state correctly.)

Another part of that problem is that the cached state isn't
much used (being unreliable, it would have been unsafe).
Those issues can be addressed in later patches.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/flash/nor/core.h

@@ -122,6 +122,10 @@ int flash_erase_address_range(struct target *target,
  */
 int flash_write(struct target *target,
 		struct image *image, uint32_t *written, int erase);
+
+/* invalidate cached state (targets may modify their own flash) */
+void nor_resume(struct target *target);
+
 /**
  * Forces targets to re-examine their erase/protection state.
  * This routine must be called when the system may modify the status.