OvmfPkg/OvmfXen: Introduce XenTimerDxe

"OvmfPkg/8254TimerDxe" is replaced with a Xen-specific
EFI_TIMER_ARCH_PROTOCOL implementation. Also remove
8259InterruptControllerDxe as it is not used anymore.

This Timer uses the local APIC timer as time source as it can work on
both a Xen PVH guest and an HVM one.

Based on the "OvmfPkg/8254TimerDxe" implementation.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1689
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20190813113119.14804-31-anthony.perard@citrix.com>

OvmfPkg/XenTimerDxe/XenTimerDxe.inf

@@ -0,0 +1,42 @@
+## @file
+# Local APIC timer driver that provides Timer Arch protocol.
+#
+# Copyright (c) 2005 - 2019, Intel Corporation. All rights reserved.<BR>
+# Copyright (c) 2019, Citrix Systems, Inc.
+#
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = XenTimerDxe
+  FILE_GUID                      = 52fe8196-f9de-4d07-b22f-51f77a0e7c41
+  MODULE_TYPE                    = DXE_DRIVER
+  VERSION_STRING                 = 1.0
+
+  ENTRY_POINT                    = TimerDriverInitialize
+
+[Packages]
+  MdePkg/MdePkg.dec
+  UefiCpuPkg/UefiCpuPkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[LibraryClasses]
+  UefiBootServicesTableLib
+  BaseLib
+  DebugLib
+  UefiDriverEntryPoint
+  LocalApicLib
+
+[Sources]
+  XenTimerDxe.h
+  XenTimerDxe.c
+
+[Protocols]
+  gEfiCpuArchProtocolGuid       ## CONSUMES
+  gEfiTimerArchProtocolGuid     ## PRODUCES
+[Pcd]
+  gEfiMdePkgTokenSpaceGuid.PcdFSBClock  ## CONSUMES
+[Depex]
+  gEfiCpuArchProtocolGuid