ArmVirtPkg: Add Platform CI and configuration for Core CI

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2570

Add new Azure Pipeline definitions to build and run ArmVirtPkg with:
  * Ubuntu GCC5
Add PyTool based build of ArmVirtPkg
Add extdep for managing the iasl dependency
Add ArmVirtPkg.ci.yaml for Core CI
Add ReadMe.md for details and instructions

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>

Reviewed-by: Shenglei Zhang <shenglei.zhang@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Bret Barkelew <bret.barkelew@microsoft.com>

ArmVirtPkg/PlatformCI/.azurepipelines/Ubuntu-GCC5.yml

@@ -0,0 +1,89 @@
+## @file
+# Azure Pipeline build file for building a platform.
+#
+# Platform: ArmVirtQemu
+# OS: Ubuntu
+# Toolchain: GCC5
+#
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+##
+trigger:
+  - master
+pr:
+  - master
+
+jobs:
+  - job: Platform_CI
+    variables:
+      package: 'ArmVirtPkg'
+      vm_image: 'ubuntu-latest'
+      should_run: true
+      run_flags: "MAKE_STARTUP_NSH=TRUE QEMU_HEADLESS=TRUE"
+
+    #Use matrix to speed up the build process
+    strategy:
+        matrix:
+          QEMU_AARCH64_DEBUG:
+            Build.File: "$(package)/PlatformCI/PlatformBuild.py"
+            Build.Arch: "AARCH64"
+            Build.Flags: ""
+            Build.Target: "DEBUG"
+            Run.Flags: $(run_flags)
+            Run: $(should_run)
+          QEMU_AARCH64_RELEASE:
+            Build.File: "$(package)/PlatformCI/PlatformBuild.py"
+            Build.Arch: "AARCH64"
+            Build.Flags: ""
+            Build.Target: "RELEASE"
+            Run.Flags: $(run_flags)
+            Run: $(should_run)
+          QEMU_AARCH64_NOOPT:
+            Build.File: "$(package)/PlatformCI/PlatformBuild.py"
+            Build.Arch: "AARCH64"
+            Build.Flags: ""
+            Build.Target: "NOOPT"
+            Run.Flags: $(run_flags)
+            Run: $(should_run)
+          QEMU_ARM_DEBUG:
+            Build.File: "$(package)/PlatformCI/PlatformBuild.py"
+            Build.Arch: "ARM"
+            Build.Flags: ""
+            Build.Target: "DEBUG"
+            Run.Flags: $(run_flags)
+            Run: $(should_run)
+          QEMU_ARM_RELEASE:
+            Build.File: "$(package)/PlatformCI/PlatformBuild.py"
+            Build.Arch: "ARM"
+            Build.Flags: ""
+            Build.Target: "RELEASE"
+            Run.Flags: $(run_flags)
+            Run: $(should_run)
+          QEMU_ARM_NOOPT:
+            Build.File: "$(package)/PlatformCI/PlatformBuild.py"
+            Build.Arch: "ARM"
+            Build.Flags: ""
+            Build.Target: "NOOPT"
+            Run.Flags: $(run_flags)
+            Run: $(should_run)
+
+    workspace:
+      clean: all
+
+    pool:
+      vmImage: $(vm_image)
+
+    steps:
+    - template: ../../../.azurepipelines/templates/platform-build-run-steps.yml
+      parameters:
+        tool_chain_tag: GCC5
+        build_pkg: $(package)
+        build_target: $(Build.Target)
+        build_arch: $(Build.Arch)
+        build_file: $(Build.File)
+        build_flags: $(Build.Flags)
+        run_flags: $(Run.Flags)
+        extra_install_step:
+        - bash: sudo apt-get install qemu
+          displayName: Install qemu
+          condition: and(gt(variables.pkg_count, 0), succeeded())