dts: nrf: Add flash controller and alignment description for nRF52840

Added flash-controller description and moved flash description to
it (for coherence). Added property for description of
the flash alignment required by write operations.
Thanks to that l-value FLASH_WRITE_BLOCK_SIZE macro
will be generated. It is useful for any component uses
the flash.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
2 files changed