mmc: atmel-mci: Incapsulate used to be a platform data into host structure

After platform data is gone, we always allocate memory for the slot
information. Incapsulate the array of the latter into the host structure,
so we allocate memory only once. This makes code simpler.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240425170900.3767990-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>