setup_sdcard.sh: [--dtb beaglebone] now replaces [--uboot bone]

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
scripts: --uboot bone -> --dtb beaglebone

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
setup_sdcard.sh: cleanup, these were converted to --dtb a long time ago

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>