tools: kwboot: Patch destination address to DDR area for SPI image

SPI/NOR kwbimage may have destination address set to 0xFFFFFFFF, which
means that the image is not downloaded to DDR but rather it is executed
directly from SPI/NOR. In this case execution address is set to SPI/NOR
area.

When patching image to UART type, change destination and execution
addresses from SPI/NOR XIP area to DDR area 0x00800000 (which is default
for A38x).

Signed-off-by: Pali Rohár <pali@kernel.org>
[ refactored ]
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>