[webrtc] Add mb configs for new bots in 2 internal masters

Master internal.client.webrtc adds 2 slaves
    'iOS64 Perf' and
    'iOS64 Release',
and master internal.tryserver.webrtc changes its slaves to be
    'ios_arm64_dbg' and
    'ios_arm64_rel'

Added configs in mb_config.pyl for the new slaves.

Bug: chromium:785924
No-Try: true
Change-Id: I1e9bec918f6517bf0ff157ebcbe90e2f56ee1261
Reviewed-on: https://webrtc-review.googlesource.com/23843
Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20724}

tools_webrtc/mb/mb_config.pyl

@@ -133,9 +133,12 @@
     },
     'internal.client.webrtc': {
       'iOS64 Debug': 'ios',
+      'iOS64 Perf': 'ios',
+      'iOS64 Release': 'ios',
     },
     'internal.tryserver.webrtc': {
-      'ios_arm64': 'ios',
+      'ios_arm64_dbg': 'ios',
+      'ios_arm64_rel': 'ios',
     },
     'tryserver.webrtc': {
       # iOS