mmc: Consolidate emmc tuning blocks

The same tuning block exists in the dw_mmc h.c and sdhci-msm.c
files. Move these into mmc.c so that they can be shared across
drivers.

Reported-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>