* For 64-bit images, use the physical address as the test pattern in test 2.
This will make it easier to diagnose faults.
* Disable test 1 by default (issue #155).
Test 2 provides the same test coverage. Test 1 may make it slightly easier
to diagnose faults with a 32-bit image, so leave it as an option.
* For 32 bit images, use the physical address to generate the offset in test 2.
Detecting a stage change and using that to reset the offset counter
could fail when the config menu was used to skip to the next test
(issue #224).
Mostly we write and read large chunks of data which will make it likely
that the data is no longer in the cache when we come to verify it. But
this is not always true, and in any case, we shouldn't rely on it.
