Using the new AAPCS function remote execution support, add support to
read from and write to SPI flash connected to a device.
This allows flashing boot code to a device.
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
[Andre: adjust to upstream changes]
Signed-off-by: Andre Przywara <osp@andrep.de>
