mmc: dw_mmc: Override blk_settings with platdata on IDMAC

When use the IDMAC, we can also want to use the pdata->blk-setting.
So if pdata->blk-setting is unset, use the default value.
if not, use the pdata->blk-setting.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Will Newton <will.newton@imgtec.com>
Signed-off-by: Chris Ball <cjb@laptop.org>