tests: Disable failing 8-core Boot Tests for Timing/Atomic

As noted here: https://gem5.atlassian.net/browse/GEM5-1217, the Atomic
and Timing Core systems are not working with 8 cores when run with a
classic or MI_example cache heirarchy. Until the root cause of this
issue can be determined. These tests are being disabled.

Change-Id: Ia19579029bd20c57cca8d225068d17c4b29f1773
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58770
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

tests/gem5/x86-boot-tests/test_linux_boot.py

@@ -238,13 +238,13 @@ run_map = {
             1: True,
             2: True,
             4: False,  # We already run this in the long (Nightly) tests.
-            8: True,
+            8: False,  # Jira: https://gem5.atlassian.net/browse/GEM5-1217
         },
         "timing": {
             1: True,
             2: True,
             4: True,
-            8: True,
+            8: False,  # Jira: https://gem5.atlassian.net/browse/GEM5-1217
         },
         "o3": {
             1: False,  # Timeout