mmc: mmc_spi: Make of_mmc_spi.c resource provider agnostic

In order to use the same driver on non-OF platforms, make
of_mmc_spi.c resource provider agnostic.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210419112459.25241-6-andriy.shevchenko@linux.intel.com


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