Add an ability to override boot mode (UEFI/Legacy) in x86 systems

[Kostr]

If the main CPU architecture is x86, besides overriding the main boot target (None/Pxe/Hdd/Cd/Diags/BiosSetup/Usb) it is also possible to override the target boot mode (None/UEFI/Legacy).

Descriptions from the https://<IP>/redfish/v1/JsonSchemas/ComputerSystem/ComputerSystem.json

                "BootSourceOverrideMode": {
                    "anyOf": [
                        {
                            "$ref": "#/definitions/BootSourceOverrideMode"
                        },
                        {
                            "type": "null"
                        }
                    ],
                    "description": "The BIOS boot mode to use when the system boots from the BootSourceOverrideTarget boot source.",
                    "longDescription": "This property shall contain the BIOS boot mode to use when the system boots from the BootSourceOverrideTarget boot source.",
                    "readonly": false,
                    "versionAdded": "v1_1_0"
                },

        "BootSourceOverrideMode": {
            "enum": [
                "Legacy",
                "UEFI"
            ],
            "enumDescriptions": {
                "Legacy": "The system boots in non-UEFI boot mode to the boot source override target.",
                "UEFI": "The system boots in UEFI boot mode to the boot source override target."
            },
            "type": "string"
        },

In case of a x86 system BootSourceOverrideMode is populated to the page https://<IP>/redfish/v1/Systems/system:

"Boot": {
  ...
  "BootSourceOverrideMode": "UEFI",
  "[email protected]": [
    "Legacy",
    "UEFI"
  ],
  ...
}

In case of POWER or other architectures, BootSourceOverrideMode is not populated.

Therefore if this variable exists under Redfish the webui-vue should provide an ability to override the target boot mode: