[nrf fromtree] tests: boards: nrf: i2c: i2c_slave: Fix DTS formatting

Add reqired empty line as indicated by the compliance check.
Add License header.
Add information about GPIO loopbacks used by the test.

Signed-off-by: Sebastian Głąb <[email protected]>
(cherry picked from commit 5501999)

Author: nordic-segl

tests/boards/nrf/i2c/i2c_slave/boards/nrf52840dk_nrf52840.overlay

@@ -1,3 +1,14 @@
+/*
+ * Copyright 2024 Nordic Semiconductor ASA
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Two loopbacks are required:
+ * P1.01 - P1.02
+ * P1.03 - P1.04
+ */
+
 / {
 	aliases {
 		i2c-slave = &i2c1;
@@ -44,6 +55,7 @@ dut_twim: &i2c0 {
 	pinctrl-1 = <&i2c0_sleep_alt>;
 	pinctrl-names = "default", "sleep";
 	clock-frequency = <I2C_BITRATE_STANDARD>;
+
 	sensor: sensor@54 {
 		reg = <0x54>;
 	};

tests/boards/nrf/i2c/i2c_slave/boards/nrf5340dk_nrf5340_cpuapp.overlay

@@ -1,3 +1,14 @@
+/*
+ * Copyright 2024 Nordic Semiconductor ASA
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Two loopbacks are required:
+ * P0.04 - P0.05
+ * P0.06 - P0.07
+ */
+
 / {
 	aliases {
 		i2c-slave = &i2c2;
@@ -44,6 +55,7 @@ dut_twim: &i2c1 {
 	pinctrl-1 = <&i2c1_sleep_alt>;
 	pinctrl-names = "default", "sleep";
 	clock-frequency = <I2C_BITRATE_STANDARD>;
+
 	sensor: sensor@54 {
 		reg = <0x54>;
 	};

tests/boards/nrf/i2c/i2c_slave/boards/nrf54h20dk_nrf54h20_cpuapp.overlay

@@ -1,3 +1,14 @@
+/*
+ * Copyright 2024 Nordic Semiconductor ASA
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Two loopbacks are required:
+ * P2.08 - P2.09
+ * P1.02 - P1.03
+ */
+
 / {
 	aliases {
 		i2c-slave = &i2c131;
@@ -48,6 +59,7 @@ dut_twim: &i2c130 {
 	pinctrl-names = "default", "sleep";
 	clock-frequency = <I2C_BITRATE_STANDARD>;
 	memory-regions = <&cpuapp_dma_region>;
+
 	sensor: sensor@54 {
 		reg = <0x54>;
 	};

tests/boards/nrf/i2c/i2c_slave/boards/nrf54h20dk_nrf54h20_cpuppr.overlay

@@ -1,3 +1,14 @@
+/*
+ * Copyright 2024 Nordic Semiconductor ASA
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Two loopbacks are required:
+ * P2.08 - P2.09
+ * P1.02 - P1.03
+ */
+
 / {
 	aliases {
 		i2c-slave = &i2c131;
@@ -47,6 +58,7 @@ dut_twim: &i2c130 {
 	pinctrl-1 = <&i2c130_sleep_alt>;
 	pinctrl-names = "default", "sleep";
 	clock-frequency = <I2C_BITRATE_STANDARD>;
+
 	sensor: sensor@54 {
 		reg = <0x54>;
 	};

tests/boards/nrf/i2c/i2c_slave/boards/nrf54l15dk_nrf54l15_cpuapp.overlay

@@ -1,3 +1,14 @@
+/*
+ * Copyright 2024 Nordic Semiconductor ASA
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Two loopbacks are required:
+ * P1.08 - P1.09
+ * P1.12 - P1.13
+ */
+
 / {
 	aliases {
 		i2c-slave = &i2c22;
@@ -47,6 +58,7 @@ dut_twim: &i2c21 {
 	pinctrl-1 = <&i2c21_sleep_alt>;
 	pinctrl-names = "default", "sleep";
 	clock-frequency = <I2C_BITRATE_STANDARD>;
+
 	sensor: sensor@54 {
 		reg = <0x54>;
 	};