ARC: AXS10x: add tool and make target to generate bsp

AXS10x boards have preloader that reads SPI flash pages and searches
special image header to fetch and load binary.

Add tool, make target (bsp-generate) to generate
update script and u-boot binary image with header for preloader.

Also add script to default environment to apply updates.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>