mmc: dw_mmc: Allow lower TMOUT value than maximum

mmc: dw_mmc: Allow lower TMOUT value than maximum

The TMOUT register is always set with a full value for every transfer,
which (with a 200MHz clock) will give a full DRTO of ~84 milliseconds.
This is normally good enough to complete the request, but setting a full
value makes it impossible to test shorter timeouts, when for example
testing data read times on different SD cards.

Add a function to set any value smaller than the maximum of 0xFFFFFF.

Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Link: https://lore.kernel.org/r/20211119155337.14341-1-marten.lindahl@axis.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>