service: device-tree node vpd to d-bus hw id data

A daemon for transferring Viable Product Data (VPD) from device-tree
nodes to D-Bus as described in the design doc @
https://gerrit.openbmc.org/c/op

service: device-tree node vpd to d-bus hw id data

A daemon for transferring Viable Product Data (VPD) from device-tree
nodes to D-Bus as described in the design doc @
https://gerrit.openbmc.org/c/openbmc/docs/+/66369

and discussed in this Technical Oversight Forum topic @
https://github.com/openbmc/technical-oversight-forum/issues/38

Tested:
Ensure 'model' and/or 'serial-number' nodes are populated in
/proc/device-tree. Can be hardcoded into platform DTS via
linux-kernel recipe if needed.

'''
After OBMC boot, calling
> busctl introspect xyz.openbmc_project.MachineContext /xyz/openbmc_project/MachineContext

produces the following output:

NAME TYPE SIGNATURE RESULT/VALUE FLAGS
...
xyz.openbmc_project.Inventory.Decorator.Asset interface - - -
.BuildDate property s "" emits-change writable
.Manufacturer property s "" emits-change writable
.Model property s "hpe,dl360" emits-change writable
.PartNumber property s "" emits-change writable
.SerialNumber property s "t5texpl" emits-change writable
...

Note: Writing to one of these properties will update the property on D-Bus without affecting the
underlying device-tree node. An 'updated' event will be fired, so Entity-Manager probes monitoring
a given property would recognize the new value and key off it.
'''

Change-Id: Id52d1fc3b26010c864c7e64d3dfdf0a2b5de9294
Signed-off-by: Chris Sides <Christopher.Sides@hpe.com>

show more ...