mmc: sdhci: Factor out some operations set to their own functions

In preparation for adding external dma support, factor out data initialization,
block info and mrq_done to their own functions.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Tested-by: Baolin Wang <baolin.wang7@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20200116105154.7685-3-faiz_abbas@ti.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>