mmc: tmio: Restructure ->set_ios() and adapt ->probe() to it

An internal power state machine were beeing used to keep ->probe() and
->set_ios() in sync. Especially for handling specific scenarios while
using CONFIG_MMC_CLKGATE. Moreover dependency to CONFIG_MMC_CLKGATE
existed to handle runtime PM properly, which we moves away from here.

By removing the state machine and instead make ->set_ios() rely on the
information provided through the function's in-parameters, the code
becomes significantly simplier.

Additonally as a part of this rework we prepares for making the runtime
PM callbacks responsible of clock gating.

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