ARM: dts: stm32: update sdmmc slew-rate in stm32mp13 pinctrl

SDMMC1/2 CK <= 50 MHz so slew-rate = <1>
A new node sdmmc1-clk-0 is added to manage the new clock pin slew-rate.

Signed-off-by: Gerald Baeza <gerald.baeza@foss.st.com>
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>