When downloading a firmware into a big flash partition the erase
operation can take a long time to be complete from few seconds to
minutes in extreme cases. During the erase the DFU gadget does not
respond to any USB setup request, the host only see a stalled USB
endpoint and cannot get responses from DFU_GETSTATE nor DFU_GETSTATUS.

After 5 seconds without any updates the host will abort the DFU
transfer and return an error (when using dfu-util).

When using the safe flag on the partition the file is first downloaded
in memory. The partition is only erased when the last chunk is received
if the partition takes more than 5 seconds to be erased then the
transfer fails.

This patch fix this issue by using the manifestation phase for safe
partitions. It's used to inform the host that the transfer is complete
and that the device will now be doing the actual erasing and writing.
Not all devices will be able to respond to DFU_GETSTATUS when in the
dfuMANIFEST state (from DFU-1.1 specification page 22).

This is far from perfect as the utility dfu-util will exit before the
erase/writing is done, but it will not report an error status if a
timeout happen during this phase.

Signed-off-by: Jules Maselbas <jmaselbas@kalray.eu>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>