flash/nor: implement protection blocks of different size than erase sector

flash/nor: implement protection blocks of different size than erase sector

Originally flash/nor infrastructure assumed protection blocks identical
to erase sectors. This assumption is not valid for many flash types.
Driver code fixed the problem either by increasing sector size to
size of protection block or by defining more protection block than
really existed in device. Both cases had drawbacks.

The change retains compatibility with the old driver.
Updated driver can set protection blocks table independent
of sector table.

Change-Id: I27f6d267528ad9ed9fe0a85f05436a8ec17603a4
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3545
Tested-by: jenkins
Reviewed-by: Steven Stallion <stallion@squareup.com>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>