u-boot-updatehub-script: Move vardeps to `do_mkimage`
u-boot-updatehub-script: Move vardeps to `do_mkimage`

Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

UpdateHub/meta-updatehub,UpdateHub/meta-updatehub,UpdateHub/meta-updatehub