Revert "change boardconfig"

This reverts commit 56f7c1e90b278f731f8aa9736c1ca67caa8a1923.
Add BOARD_FLASH_BLOCK_SIZE to get rid of compile error
/bin/bash: (((5272614336 / 100) - 1) / img_blocksize + 1) * img_blocksize: division by 0 (error token is "img_blocksize + 1) * img_blocksize")

Change-Id: I62d46619ee13fa8490af2dedb9fbb2aa46a7e333