mmc: sdhci: Call mmc_request_done() from IRQ handler if possible

In preparation for removing finish_tasklet, call mmc_request_done() from
the IRQ handler if possible. That will alleviate the potential loss of
performance from shifting away from finish_tasklet.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>