riscv: dts: sifive unmatched: Expose the board ID eeprom

Mark it as read-only as it is factory-programmed with identifying
information, and no executable nor configuration:
- eth MAC address
- board model (PCB version, BoM version)
- board serial number
Accidental modification would cause misidentification which could brick
the board, so marking read-only seem like both a safe and non-constraining
choice.
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

@@ -59,6 +59,16 @@ temperature-sensor@4c {
 		interrupts = <6 IRQ_TYPE_LEVEL_LOW>;
 	};
 
+	eeprom@54 {
+		compatible = "microchip,24c02", "atmel,24c02";
+		reg = <0x54>;
+		vcc-supply = <&vdd_bpro>;
+		label = "board-id";
+		pagesize = <16>;
+		read-only;
+		size = <256>;
+	};
+
 	pmic@58 {
 		compatible = "dlg,da9063";
 		reg = <0x58>;