NetworkPkg: introduce include file for dynamic PCDs

Introduce an include file with dynamic PCDs to simplify the usage of
the network stage. This allows us to stop manually adding
`PcdIPv4PXESupport` and `PcdIPv6PXESupport` to the DSC file.

`NETWORK_IP4_ENABLE` and `NETWORK_IP6_ENABLE` are not used because
PXEv4 and PXEv6 boot support can be controlled from the QEMU command
line.

Cc: Saloni Kasbekar <saloni.kasbekar@intel.com>
Cc: Zachary Clark-williams <zachary.clark-williams@intel.com>
Signed-off-by: Aleksandr Goncharov <chat@joursoir.net>

NetworkPkg/Network.dsc.inc

@@ -28,6 +28,9 @@
 [PcdsFixedAtBuild]
 !include NetworkPkg/NetworkPcds.dsc.inc
 
+[PcdsDynamicDefault]
+!include NetworkPkg/NetworkDynamicPcds.dsc.inc
+
 [LibraryClasses]
 !include NetworkPkg/NetworkLibs.dsc.inc
 

NetworkPkg/NetworkDynamicPcds.dsc.inc

@@ -0,0 +1,20 @@
+## @file
+# Network DSC include file for [PcdsDynamic*] section of all Architectures.
+#
+# This file can be included to the [PcdsDynamic*] section(s) of a platform DSC file
+# by using "!include NetworkPkg/NetworkDynamicPcds.dsc.inc" to specify PCD settings
+# according to the value of flags described in "NetworkDefines.dsc.inc".
+#
+# Copyright (c) 2024, Aleksandr Goncharov. All rights reserved.<BR>
+#
+#    SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+#
+# IPv4 and IPv6 PXE Boot support.
+#
+!if $(NETWORK_ENABLE) == TRUE
+  gEfiNetworkPkgTokenSpaceGuid.PcdIPv4PXESupport|0x01
+  gEfiNetworkPkgTokenSpaceGuid.PcdIPv6PXESupport|0x01
+!endif