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installboot(8) to write u-boot images to SPI NOR and other types of raw flash devices: input-block-size, input-pad-size, output-size, and output-block-size. Add the ability to create aliases for install objects, useful for when e.g. sdmmc and emmc share the same steps. Tested on an A20-OLinuXino-LIME2-e16Gs16M by bouyer@. XXX pullup netbsd-9