Boot Source Override feature problems

[Konstantin Aladyshev]

We need to have two `xyz.openbmc_project.Object.Enable` interfaces:
1) one that stores information whether the BootSourceOverride feature
is enabled or not,
2) another one that stores information whether the BootSourceOverride
feature is permanent or one_time.

The current implementation has only 1), proposed design has both 1) and 2):
```
 /xyz/openbmc_project/control/host0/boot:
      - Interface: xyz.openbmc_project.Control.Boot.Source
      - Interface: xyz.openbmc_project.Control.Boot.Mode
      - Interface: xyz.openbmc_project.Control.Boot.Type
      - Interface: xyz.openbmc_project.Object.Enable              <---------  1)
 /xyz/openbmc_project/control/host0/boot/one_time:
      - Interface: xyz.openbmc_project.Object.Enable              <---------  2)
```

Also earlier there were two sets of Boot.Source/Boot.Mode/Boot.Type
settings. But the second one isn't really necessary as the
BootSourceOverride feature doesn't fallback to permanent override
after one-time override. So we need to keep only one set of
Boot.Source/Boot.Mode/Boot.Type settings.

Best regards,
Konstantin Aladyshev