tools: Add Marvell recovery image download script

Introduce the recovery image download script for usage with
Marvell Armada SoC families (excepting 37xx family).
Since Marvell BootROM uses a sliding window in UART buffer
for detecting escape sequence during the boot, it's easier
to interrupt the normal boot flow by sending a long stream
of chained escape sequences to the serial port instead of
periodically sending a single escape sequence as it is done
by kwboot utility.
Additional benefit of using this script is the ability to
adjust the escape sequence stream length withoiut need for
compilation.

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Igal Liberman <igall@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>