riscv: dts: thead: Add IO labels for the IO expansion on I2C1

Add labels for GPIOs on the IO expansion chip on the I2C1 bus.

Link: https://lore.kernel.org/r/20260714074515.1959352-5-zhengxingda@iscas.ac.cn
Reviewed-by: Drew Fustini <fustini@kernel.org>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
[Icenowy: Splitted off the patch adding all 3 IO expansions]
Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
[fustini: align ioexp2 gpio-line-names with schematic]
Signed-off-by: Drew Fustini <fustini@kernel.org>

arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts

@@ -128,6 +128,14 @@ ioexp2: gpio@18 {
 		reg = <0x18>;
 		gpio-controller;
 		#gpio-cells = <2>;
+		gpio-line-names = "",
+				  "cam0_reset",
+				  "cam1_reset",
+				  "cam2_reset",
+				  "wl_host_wake_dev",
+				  "bt_resetn",
+				  "",
+				  "bt_host_wake_dev";
 	};
 };