ARC: HSDK: Add tool and make target to generate bsp

HSDK board has preloader that reads SPI flash pages and searches
for a 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>