mmc: dw_mmc: Remove the public dw_mmc header file

There are currently no external users of the public dw_mmc header file,
except the dw_mmc driver itself. Therefore let's move the definitions from
the public dw_mmc header file into the existing private dw_mmc header file
and then remove the public one.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>