ARM: dts: stm32: Add additional init state for SDMMC1 pins

Add "init" mux option for SDMMC1, where the CMD, CK, CKIN lines are not
configured, so they can be claimed as GPIOs early on in driver probe().
This is used for probing optional voltage level translator.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Ludovic Barre <ludovic.barre@st.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: linux-stm32@st-md-mailman.stormreply.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>