mmc: tmio_mmc: Fixup system PM suspend lock-up

At system PM suspend, the tmio core accessed the internal registers of
the controller without first moving the device into active state. This
caused a lock-up in system PM suspend phase.

The reason for the register access were masking of IRQs. Since that is
managed via the runtime PM suspend path, let's just re-use that path
for system PM suspend.

In other words force the device into runtime PM suspend state at system
PM suspend and restore it to active state at system PM resume.

Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>