Add Transfer Size Option to tftp

Add Transfer Size Option to tftp

Optionally add RFC 2349 "Transfer Size Option", so we can minimize the
time spent sending data over the UART (now print a single line during a
tftp transfer).

 - If turned on (CONFIG_TFTP_TSIZE), U-Boot asks for the size of the file.
 - if receives the file size, a single line (50 chars) are printed.
     one hash mark == 2% of the file downloaded.
 - if it doesn't receive the file size (the server doesn't support RFC
     2349, prints standard hash marks (one mark for each UDP frame).

Signed-off-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>