Replace:
DT_FLASH_ERASE_BLOCK_SIZE ->
DT_PROP(DT_CHOSEN(zephyr_flash), erase_block_size)
DT_FLASH_WRITE_BLOCK_SIZE ->
DT_PROP(DT_CHOSEN(zephyr_flash), write_block_size)
As this allows us to phase out the old generator.
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>