mmc: rtsx: Revert "mmc: rtsx: add support for pre_req and post_req"

This reverts commit c42deffd.

commit <mmc: rtsx: add support for pre_req and post_req> did use
mutex_unlock() in tasklet, but mutex_unlock() can't be used in
tasklet(atomic context). The driver needs to use mutex to avoid
concurrency, so we can't use tasklet here, the patch need to be
removed.

The spinlock host->lock and pcr->lock may deadlock, one way to solve
the deadlock is remove host->lock in sd_isr_done_transfer(), but if
using workqueue the we can avoid using the spinlock and also avoid
the problem.

Signed-off-by: Micky Ching <micky_ching@realsil.com.cn>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>