mmc: mmc_test: Add re-tuning test

mmc: mmc_test: Add re-tuning test

Add a test to repeatedly re-tune in between random reads. The test is
non-destructive of data on the card and runs for 30 seconds. It can be
repeated to test for longer durations.

If re-tuning is not supported, the test is skipped.

Example:

  # echo 'mmc1:0001' >  /sys/bus/mmc/drivers/mmcblk/unbind
  # echo 'mmc1:0001' > /sys/bus/mmc/drivers/mmc_test/bind
  [   36.642257] mmc_test mmc1:0001: Card claimed for testing.
  # cat /sys/kernel/debug/mmc1/mmc1\:0001/testlist | grep tuning
  52:     Re-tuning reliability
  # echo 52 > /sys/kernel/debug/mmc1/mmc1\:0001/test
  [   91.522555] mmc1: Starting tests of card mmc1:0001...
  [   91.528425] mmc1: Test case 52. Re-tuning reliability...
  [  121.536682] mmc1: Result: OK
  [  121.539572] mmc1: Tests completed.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20231214090902.43628-1-adrian.hunter@intel.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>