tools: kwboot: Prevent waiting indefinitely if no xmodem reply is received

tools: kwboot: Prevent waiting indefinitely if no xmodem reply is received

Currently if BootROM fails to respond with ACK/NAK to a xmodem block, we
will be waiting indefinitely for such response.

Make sure that we only wait at most 1 second (blk_rsp_timeo) for ACK/NAK
for each block in case non-xmodem text output is not being expected.
Interpret this timeout expiration as NAK, to try to send the block
again.

On the other hand, if timeout expires without ACK while some non-xmodem
output was already received (DDR training output, for example), we know
that the block was received, since the code is being executed, so in
this case exit with ETIMEDOUT.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>