boards: frdm_k82f: Enable adc instance and pinmux

Enables the adc instance and pinmux associated with arduino header pin
A2 on the frdm_k82 board. Adds adc to the board yaml to ensure we build
adc samples/tests for this board in CI.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>

boards/arm/frdm_k82f/frdm_k82f.dts

@@ -106,6 +106,10 @@
 	};
 };
 
+&adc0 {
+	status = "okay";
+};
+
 &gpioa {
 	status = "okay";
 };

boards/arm/frdm_k82f/frdm_k82f.yaml

@@ -9,6 +9,7 @@ toolchain:
 ram: 192
 flash: 256
 supported:
+  - adc
   - arduino_gpio
   - gpio
   - i2c

boards/arm/frdm_k82f/pinmux.c

@@ -77,6 +77,11 @@ static int frdm_k82f_pinmux_init(struct device *dev)
 	pinmux_pin_set(portc, 15, PORT_PCR_MUX(kPORT_MuxAlt3));
 #endif
 
+#if DT_NODE_HAS_STATUS(DT_NODELABEL(adc0), okay)
+	/* ADC0_SE15 */
+	pinmux_pin_set(portc,  1, PORT_PCR_MUX(kPORT_PinDisabledOrAnalog));
+#endif
+
 	return 0;
 }