mmc: core: Extend re-use of __mmc_poll_for_busy()

Via __mmc_poll_for_busy() we end up polling with the ->card_busy() host ops
or by sending the CMD13. To allow polling of different types, which is
needed to support a few new SD card features, let's rework the code around
__mmc_poll_for_busy() to make it more generic.

More precisely, let __mmc_poll_for_busy() take a pointer to a callback
function as in-parameter, which it calls to poll for busy state completion.
Additionally, let's share __mmc_poll_for_busy() to allow it to be re-used
outside of mmc_ops.c. Subsequent changes will make use of it.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Acked-by: Avri Altman <avri.altman@wdc.com>
Link: https://lore.kernel.org/r/20210504161222.101536-5-ulf.hansson@linaro.org