ARM: dts: stm32: update eMMC configuration for stm32mp157c-ev1

Update the sdmmc2 node for eMMC support on eval board stm32mp157c-ev1.
- update slew-rate for pin configuration
- update "vqmmc-supply"
- remove "st,sig-dir"
- add mandatory "pinctrl-names"
- add "mmc-ddr-3_3v"

This patch solve the eMMC detection issue for command "mmc dev 1".

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/dts/stm32mp157c-ed1-u-boot.dtsi b/arch/arm/dts/stm32mp157c-ed1-u-boot.dtsi
index 4953a0d..b2ac494 100644
--- a/arch/arm/dts/stm32mp157c-ed1-u-boot.dtsi
+++ b/arch/arm/dts/stm32mp157c-ed1-u-boot.dtsi
@@ -174,7 +174,10 @@
 
 &sdmmc2_b4_pins_a {
 	u-boot,dm-spl;
-	pins {
+	pins1 {
+		u-boot,dm-spl;
+	};
+	pins2 {
 		u-boot,dm-spl;
 	};
 };