Export the part number and serial number

This commit exposes the eMMC's part name and serial number over the
appropriate D-Bus interface, so that it can be exposed over Redfish in
bmcweb.

Tested:
$ busctl introspect xyz.openbmc_project.eStoraged \
  /xyz/openbmc_project/inventory/storage/mmcblk0
  ...
  xyz.openbmc_project.Inventory.Decorator.Asset    interface -         -                                        -
.PartNumber                                      property  s         "ABCDEF"                                 emits-change
.SerialNumber                                    property  s         "123456abcd"                             emits-change
  ...
$ wget -qO- http://localhost:80/redfish/v1/Chassis/DC_SCM/Drives/mmcblk0
{
  "@odata.id": "/redfish/v1/Chassis/DC_SCM/Drives/mmcblk0",
  "@odata.type": "#Drive.v1_7_0.Drive",
  "CapacityBytes": 15634268160,
  "Id": "mmcblk0",
  "Links": {
    "Chassis": {
      "@odata.id": "/redfish/v1/Chassis/DC_SCM"
    }
  },
  "Name": "Name",
  "PartNumber": "ABCDEF",
  "PhysicalLocation": {
    "PartLocation": {
      "LocationType": "Embedded"
    }
  },
  "SerialNumber": "123456abcd",
  "Status": {
    "State": "Enabled"
  }
}

Signed-off-by: John Wedig <johnwedig@google.com>
Change-Id: I1d17f08b99907620b5f2c73fdaeacc84950ce64e
diff --git a/include/util.hpp b/include/util.hpp
index 2834950..a6af6ed 100644
--- a/include/util.hpp
+++ b/include/util.hpp
@@ -21,6 +21,18 @@
  */
 uint8_t findPredictedMediaLifeLeftPercent(const std::string& sysfsPath);
 
+/** @brief Get the part number (aka part name) for the storage device
+ *  @param[in] sysfsPath - The path to the linux sysfs interface.
+ *  @return part name as a string (or "unknown" if it couldn't be retrieved)
+ */
+std::string getPartNumber(const std::filesystem::path& sysfsPath);
+
+/** @brief Get the serial number for the storage device
+ *  @param[in] sysfsPath - The path to the linux sysfs interface.
+ *  @return serial name as a string (or "unknown" if it couldn't be retrieved)
+ */
+std::string getSerialNumber(const std::filesystem::path& sysfsPath);
+
 /** @brief Look for the device described by the provided StorageData.
  *  @details Currently, this function assumes that there's only one eMMC.
  *    When we need to support multiple eMMCs, we will put more information in