support runtime update of BIOS attributes

Register the BIOSConfig/PendingAttributes signal and when the out of band
redfish user updates the BIOS attributes, the pldm daemon should process and
check the PendingAttributes porperty, and then update the
BIOSConfig/BaseBIOSTable property and the BIOS table.

Tested: test JSON with
        https://gist.github.com/lxwinspur/2afffff2e445fddf90dfed6eceef4014
Type.Enumeration:
~#: busctl set-property xyz.openbmc_project.BIOSConfigManager
    /xyz/openbmc_project/bios_config/manager
	xyz.openbmc_project.BIOSConfig.Manager PendingAttributes a\{s\(sv\)\} 1
	"Led" "xyz.openbmc_project.BIOSConfig.Manager.AttributeType.Enumeration" s
	"xyz.openbmc_project.Led.Physical.Action.On"
~#: pldmtool bios getbiostable -t 2
    PLDM AttributeValueTable:
    ... ...
    AttributeHandle: 3
 	    AttributeType: BIOSEnumeration
	    NumberOfCurrentValues: 1
	    CurrentValueStringHandleIndex[0] = 0, StringHandle = On
    ... ...

Type.String
~#: busctl set-property xyz.openbmc_project.BIOSConfigManager
    /xyz/openbmc_project/bios_config/manager
	xyz.openbmc_project.BIOSConfig.Manager PendingAttributes a\{s\(sv\)\} 1
	"Model" "xyz.openbmc_project.BIOSConfig.Manager.AttributeType.String" s
	"testModel"
~#: pldmtool bios getbiostable -t 2
    PLDM AttributeValueTable:
    AttributeHandle: 0
	    AttributeType: BIOSString
	    CurrentStringLength: 10
	    CurrentString: testModel
	... ...

Type.Integer
~#: busctl set-property xyz.openbmc_project.BIOSConfigManager
    /xyz/openbmc_project/bios_config/manager
	xyz.openbmc_project.BIOSConfig.Manager PendingAttributes a\{s\(sv\)\} 1
	"OUTLET" "xyz.openbmc_project.BIOSConfig.Manager.AttributeType.Integer" x
	1000
~#: pldmtool bios getbiostable -t 2
    ... ...
	AttributeHandle: 2
	    AttributeType: BIOSInteger
	    CurrentValue: 1000
	... ...

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I4d4d2941e6c9bfa7f6fccb664db1580f2ffc9c9f
diff --git a/libpldmresponder/bios_config.hpp b/libpldmresponder/bios_config.hpp
index 8782640..b10ca78 100644
--- a/libpldmresponder/bios_config.hpp
+++ b/libpldmresponder/bios_config.hpp
@@ -48,6 +48,9 @@
                MenuPath, CurrentValue, DefaultValue, Option>;
 using BaseBIOSTable = std::map<AttributeName, BIOSTableObj>;
 
+using PendingObj = std::tuple<AttributeType, CurrentValue>;
+using PendingAttributes = std::map<AttributeName, PendingObj>;
+
 /** @class BIOSConfig
  *  @brief Manager BIOS Attributes
  */
@@ -220,6 +223,23 @@
     /** @brief Update the BaseBIOSTable property of the D-Bus interface
      */
     void updateBaseBIOSTableProperty();
+
+    /** @brief Listen the PendingAttributes property of the D-Bus interface and
+     *         update BaseBIOSTable
+     */
+    void listenPendingAttributes();
+
+    /** @brief Find attribute handle from bios attribute table
+     *  @param[in] attrName - attribute name
+     *  @return attribute handle
+     */
+    uint16_t findAttrHandle(const std::string& attrName);
+
+    /** @brief Listen the PendingAttributes property of the D-Bus interface
+     * and update BaseBIOSTable
+     *  @param[in] msg - Data associated with subscribed signal
+     */
+    void constructPendingAttribute(const PendingAttributes& pendingAttributes);
 };
 
 } // namespace bios