product/synquacer: enable DDR DQS gate training workaround

This commit enables the workaround for the DDR DQS gate training
issue of the DDR PHY.
Without this workaround, there is a possibility that DQS gate
training ends up in incorrect state.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Change-Id: Icba7c151cd80875dcdf26f579c58ea3da9b86c99