mmc: dw_mmc: Convert to mmc_send_tuning()

Instead of having a local hack taking care of sending the tuning
command and as well to verify the response pattern, let's convert to
the common mmc_send_tuning() API.

This change affects the Exynos variant, since it's the only one which
support the dw_mmc's ->execute_tuning() callback.

It's seems like dw_mmc internal logic expects failed data transfers to
be ended using a stop command. Let the tuning requests also fall into
this category, since there are data transfer involved.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Tested-by: Alim Akhtar <alim.akhtar@samsung.com>