ARM: dts: uniphier: remove U-Boot own EEPROM compatible and property

The compatible string "i2c-eeprom" is U-Boot own compatible, which
has never been approved by the DT community. "u-boot,i2c-offset-len"
is also a U-Boot own hack.

Linux adds "atmel,*" as generic compatibles, and U-Boot also followed
it by commit d7e28918 ("i2c_eeprom: Add reading support").

The U-Boot own hack is no longer needed. Just sync with Linux.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>