mpc85xx: change legacy "eeprom" compatible

silences the following message:
> eeprom 0-0051: eeprom driver is deprecated, please use at24 instead

The chip was likely a Dallas Semiconductor and later MAXIM part
before Analog Devices, Inc. bought MAXIM.

From the datasheet:

"The DS28CN01 combines 1024 bits of EEPROM with challenge-and-response
authentication security implemented with the FIPS 180-1/180-2 and
ISO/IEC 10118-3 Secure Hash Algorithm (SHA-1)."

...

"Write Access Requires Knowledge of the Secret
and the Capability of Computing and Transmitting
a 160-Bit MAC as Authorization"

OpenWrt doesn't use it. There's no in-kernel driver
from what I know. Let's document that the chip is
at the location.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/mpc85xx/files/arch/powerpc/boot/dts/hiveap-330.dts

@@ -183,10 +183,14 @@
 #endif
 			};
 
-			/* Most likely SoC boot config */
 			eeprom@51 {
-				compatible = "eeprom";
+				/*
+				 * 1Kbit I2C/SMBus EEPROM with SHA-1 Engine
+				 * Aerohive calls it "dallas".
+				 */
+				compatible = "adi,ds28cn01";
 				reg = <0x51>;
+				read-only;
 			};
 		};