fastboot: default to logical-block-size 4096
fastboot: default to logical-block-size 4096

Mainline U-Boot without uboot-imx additions does not report a
logical-block-size. Default to 4096 in this case to make the -raw2sparse
feature compatible with these U-Boot versions.

Signed-off-by: Matthias Schiffer <3e83e6805cb27b6d05f60e534f59e1793bc7c8bf@tq-group.com>

NXPmicro/mfgtools,NXPmicro/mfgtools,NXPmicro/mfgtools