Use `FLASH_PTR` macro to convert a flash address to a const pointer.
For real hardware it is just a cast, for emulator we subtract the
`FLASH_ORIGIN` and use it as index into the memory mapped flash file.
Make write access to flash with volatile pointers
Also use FLASH_PTR in DebugMemory* for now. This allows for reading and
writing the flash in the emulator or just crash it by reading outside
the flash...
Instead of reflashing the whole storage, we use a designated area
in the second storage block, where we mark each PIN failure by a
single zero bit. This is because one can set bits in flash to zero but
not to one. If the PIN was entered successfully the whole word is
set to zero and the next word stores the new PIN failure counter.
This diff contains three changes.
1. Make timing isPinCorrect independent of storage.pin, to avoid timing attacks
2. Only update failed PIN counter if the user entered a PIN.
Of course, the fail counter is still incremented, before the PIN is checked.
3. Don't cache the PIN, but just the fact that the PIN was entered. The
cache should be in sync with storage.pin in any case.
