nand/fileio: change prototype of nand_fileio_start()

nand/fileio: change prototype of nand_fileio_start()

To prepare for handling TCL return values consistently, all calls
to command_print/command_print_sameline should be ready to switch
to CMD as first parameter.

Change prototype of nand_fileio_start() to pass CMD instead of
CMD_CTX.

This change was part of http://openocd.zylin.com/1815 from Paul
Fertser and has been extracted and rebased to simplify the review.

Change-Id: I7993f6aba997a2d2917949563651c8d0c213730d
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5052
Tested-by: jenkins