med: Add configure inventory commands

med: Add configure inventory commands

Default inventory information is fetched from dmi table.
Most of embedded devices do not run EFI bootloader hence dmi information
will not be available in /sys/class/dmi

- Add `configure inventory` commands
- Add `unconfigure inventory` commands
- New code is dependent on enable-lldpmed
- Add write support on lldpctl atoms
- Add support for setting inventory configuration in daemon
- Refactor `lldp_med` to assign `c_med_sw` only once.
  We have the configurability of inventory information, So
  it is not required for daemon to keep assigning `c_med_sw`