mmc: mmc_spi: remove custom DMA mapped buffers

mmc: mmc_spi: remove custom DMA mapped buffers

There is no need to duplicate what SPI core or individual controller
drivers already do, i.e. mapping the buffers for DMA capable transfers.

Note, that the code, besides its redundancy, was buggy: strictly speaking
there is no guarantee, while it's true for those which can use this code
(see below), that the SPI host controller _is_ the device which does DMA.

Also see the Link tags below.

Additional notes. Currently only two SPI host controller drivers may use
premapped (by the user) DMA buffers:

  - drivers/spi/spi-au1550.c

  - drivers/spi/spi-fsl-spi.c

Both of them have DMA mapping support code. I don't expect that SPI host
controller code is worse than what has been done in mmc_spi. Hence I do
not expect any regressions here. Otherwise, I'm pretty much sure these
regressions have to be fixed in the respective drivers, and not here.

That said, remove all related pieces of DMA mapping code from mmc_spi.

Link: https://lore.kernel.org/linux-mmc/c73b9ba9-1699-2aff-e2fd-b4b4f292a3ca@raspberrypi.org/
Link: https://stackoverflow.com/questions/67620728/mmc-spi-issue-not-able-to-setup-mmc-sd-card-in-linux
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20231207221901.3259962-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>