fdts: stm32mp1: add I2C2 pins in the pinctrl

Some STM32MP1‐based boards, like Seeed Studio’s SoM‐STM32MP157C, have
the SoC connected to the PMIC via I2C2 instead of I2C4 (which is used on
the official ST development boards). This commit brings TF‑A one step
closer to boot on such boards.

The pins used, PH4 and PH5, are described in a new pinctrl node named
“i2c2-0”, AKA phandle “i2c2_pins_a”. These names are identical to their
Linux kernel counterparts (commit
7af08140979a6e7e12b78c93b8625c8d25b084e2).
Signed-off-by: Grzegorz Szymaszek <gszymaszek@short.pl>
Change-Id: Ief6f0a632cfa992dcf3fed95d266ad6a07a96fe0

fdts/stm32mp15-pinctrl.dtsi

@@ -31,6 +31,16 @@
 		};
 	};
 
+	i2c2_pins_a: i2c2-0 {
+		pins {
+			pinmux = <STM32_PINMUX('H', 4, AF4)>, /* I2C2_SCL */
+				 <STM32_PINMUX('H', 5, AF4)>; /* I2C2_SDA */
+			bias-disable;
+			drive-open-drain;
+			slew-rate = <0>;
+		};
+	};
+
 	qspi_clk_pins_a: qspi-clk-0 {
 		pins {
 			pinmux = <STM32_PINMUX('F', 10, AF9)>; /* QSPI_CLK */