mmc: sdhci-sprd: Set the missing MMC_CAP_WAIT_WHILE_BUSY flag

The Spreadtrum host controller supports HW busy detection for commands with
R1B responses, but also for I/O operations. This means when the host gets a
transfer complete event, that always indicates the busy signal is released.

Let's inform the mmc core about this, via setting the corresponding
MMC_CAP_WAIT_WHILE_BUSY flag, as to remove some redundant software busy
polling.

Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/96f16647f6a6e8cb058c44e46c61b122df027059.1582535202.git.baolin.wang7@gmail.com


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