Adding support for sys-eeprom tool for x86_64 platforms

Ticket: ONIE-19
Reviewed By: curt, scotte
Testing Done: Tested on dell_s6000

Currently onie doesnt have a sys_eeprom tool. In powerpc based platforms, we
have U-boot from we can access the eeprom, and hence we could live without
this tool. But with x86, there is no u-boot, and eeprom access will now
have to be from ONIE.
Updates:
- Added support for Service Tag TLV
- Changed name from sys-eeprom to onie-syseeprom