board: dragonboard410c: Use BOOTSTD instead of DISTRO_DEFAULTS

board: dragonboard410c: Use BOOTSTD instead of DISTRO_DEFAULTS

Reduce the environment size by using standard boot instead of distro boot.
It uses faster bootdevs first by default (eMMC -> SD -> USB -> Network), so
set "boot_targets" to keep the current ordering (USB -> SD -> eMMC ->
Network). Perhaps this should be changed for consistency, but for now this
keeps the behavior similar to before.

Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by:
Link: https://lore.kernel.org/r/20250407-db410c-fixes-v1-10-524aefbc8bb4@linaro.org
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>