Use mobo's object system iface to find mobo path.

This change use system interface to find the inventory object path
of the root board in the system. This replaces the `ReScan`
method to get the root object path. The `ReScan` implementation in
EntityManager never upstreamed and that CL was abandoned.
CL: https://gerrit.openbmc.org/c/openbmc/entity-manager/+/46128

TESTED:

busctl get-property xyz.openbmc_project.Smbios.MDR_V2 \
> /xyz/openbmc_project/inventory/system/chassis/motherboard/cpu0 \
> xyz.openbmc_project.Association.Definitions Associations
a(sss) 1 "chassis" "processors" "/xyz/openbmc_project/inventory/system/board/motherboard"

busctl get-property xyz.openbmc_project.Smbios.MDR_V2 \
> /xyz/openbmc_project/inventory/system/chassis/motherboard/cpu1 \
> xyz.openbmc_project.Association.Definitions Associations
a(sss) 1 "chassis" "processors" "/xyz/openbmc_project/inventory/system/board/motherboard"

busctl  --verbose get-property xyz.openbmc_project.ObjectMapper \
/xyz/openbmc_project/inventory/system/board/motherboard/processors \
xyz.openbmc_project.Association endpoints
ARRAY "s" {
        STRING "/xyz/openbmc_project/inventory/system/chassis/motherboard/cpu0";
        STRING "/xyz/openbmc_project/inventory/system/chassis/motherboard/cpu1";
};

Signed-off-by: Gobinath Krishnamoorthy <gobinathk@google.com>
Change-Id: Idc6f8c58324c7618a2c4c5a2c4079599c7c29cf4
2 files changed