Older tftp server don't send the file size.
Then tftpfs needs temporary place to store the file.
mount ramfs and then tftpfs in a own mount point
Signed-off-by: Jan Remmet <j.remmet@phytec.de>
Tested-by: Wadim Egorov <w.egorov@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>