NetworkPkg:Add scriptable configuration to iSCSI driver by leveraging x-UEFI.

v2:
Add error handling if can not create Attempts in driver entry point.
Since we support to define a macro be a PCD value, we enhance our code
by modifying the structure in IFR_NVDATA. This effect code logic mainly
in Creating Keywords,Convert IFR NvData To AttemptConfigData ByKeyword and
reverse function.
Fix typo errors and sync based on the latest code.

Enable iSCSI keywords configuration based on x-UEFI
name space. we introduce new PCD to control the attempt
numbers which will be created in non activated state, besides
the Attempt name is changed to READ_ONLY attribute in UI.
We can invoke KEYWORD HANDLER Protocol to configure
the related keywords.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Zhang Lubo <lubo.zhang@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Wu Jiaxin jiaxin.wu@intel.com

NetworkPkg/IScsiDxe/IScsiDriver.h

@@ -1,7 +1,7 @@
 /** @file
   The header file of IScsiDriver.c.
 
-Copyright (c) 2004 - 2015, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2004 - 2017, Intel Corporation. All rights reserved.<BR>
 (C) Copyright 2017 Hewlett Packard Enterprise Development LP<BR>
 
 This program and the accompanying materials
@@ -68,7 +68,6 @@ typedef struct {
   LIST_ENTRY      AttemptConfigs;       // User configured Attempt list.
   CHAR8           InitiatorName[ISCSI_NAME_MAX_SIZE];
   UINTN           InitiatorNameLength;
-  VOID            *NewAttempt;          // Attempt is created but not saved.
 } ISCSI_PRIVATE_DATA;
 
 extern ISCSI_PRIVATE_DATA                 *mPrivate;