riscv: dts: sifive unmatched: Name gpio lines

Follow the pin descriptions given in the version 3 of the board schematics.
Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/boot/dts/sifive/hifive-unmatched-a00.dts

@@ -247,4 +247,8 @@ &pwm1 {
 
 &gpio {
 	status = "okay";
+	gpio-line-names = "J29.1", "PMICNTB", "PMICSHDN", "J8.1", "J8.3",
+		"PCIe_PWREN", "THERM", "UBRDG_RSTN", "PCIe_PERSTN",
+		"ULPI_RSTN", "J8.2", "UHUB_RSTN", "GEMGXL_RST", "J8.4",
+		"EN_VDD_SD", "SD_CD";
 };