dts: Remove ifdef CONFIG_FS_FLASH_STORAGE_PARTITION from dts files

Remove the ifdef related to CONFIG_FS_FLASH_STORAGE_PARTITION.  There
shouldn't be any harm in always having the partition around as we'll
just generate the defines related to and most applications will ignore
them.

Helps get one step closer to have DTS not depend on Kconfig.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>