The variable 'dualboot' (and 'singlemtdsys' for CC6UL) was restored
after the bootcmd that runs the first time after programming U-Boot runs
fastboot again to resume the script.
This is ok for the CC6UL but not for the rest of platforms, that run the
partition script on the bootcmd, *before* running fastboot.
Restore the variables for all platforms in the bootcmd right after
resetting the environment.
Signed-off-by: Hector Palacios <hector.palacios@digi.com>