utils: Add the omnia-eeprom utility

utils: Add the omnia-eeprom utility

Add a new utility, `omnia-eeprom`, which can be used to print / set
EEPROM fields on Turris Omnia.

One example when this utility might be useful is if the board
experiences random crashes due to newer versions of the DDR training
algorithm in newer U-Boot. The user can change the DDR speed from 1600K
to 1333H to solve these issues, with

  ```
  omnia-eeprom set ddr_speed 1333H
  ```

Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://github.com/openwrt/openwrt/pull/16264
Signed-off-by: Robert Marko <robimarko@gmail.com>