In cases when SDIO IRQs have been enabled, runtime suspend is prevented by
the driver. However, this still means msdc_runtime_suspend|resume() gets
called during system suspend/resume, via pm_runtime_force_suspend|resume().

This means during system suspend/resume, the register context of the mtk-sd
device most likely loses its register context, even in cases when SDIO IRQs
have been enabled.

To re-enable the SDIO IRQs during system resume, the mtk-sd driver
currently relies on the mmc core to re-enable the SDIO IRQs when it resumes
the SDIO card, but this isn't the recommended solution. Instead, it's
better to deal with this locally in the mtk-sd driver, so let's do that.
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>