flash: stop caching protection state

flash: stop caching protection state

There are a million reasons why cached protection state might
be stale: power cycling of target, reset, code executing on
the target, etc.

The "flash protect_check" command is now gone. This is *always*
executed when running a "flash info".

As a bonus for more a more robust approach, lots of code could
be deleted.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>