LU-12186 ec: add necessary structure member for EC file

LU-12186 ec: add necessary structure member for EC file

Added basic structure members for erasure-coding layout.

Test-Parameters: trivial
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I697dc144877d6c5fbe9335dc721200e43749f5d9
Reviewed-on: https://review.whamcloud.com/38319
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>