Build - Allow override of device asserts, including multi-device support.

Set in board file with TARGET_OTA_ASSERT_DEVICE.
(cherry-picked from commit 0f452f21fc9323b9d1fe746161761cf40aaa5030)

Change-Id: I05035d3f393fcff62f582d1ac4ec94bc43cb10f2
Signed-off-by: STELIX <ssspinni@gmail.com>