ArmPkg: Enable AuditMode for Uncrustify CI checks

Uncrustify checks are too rigid, making them counter-productive:

- it leads to code that is arguably harder to parse visually (e.g.,
  the changes to ArmPkg/Include/Chipset/AArch64Mmu.h in commit
  429309e0c6b74792)
- it forces indentation-only changes to code in the vicinity of actual
  changes, making the code history more bloated than necessary (see
  commit 7f198321eec0f520373 for an example)
- finding out from the web UI what exactly Uncrustify objected to is not
  straight-forward.

So let's enable AuditMode for ArmPkg, so that interested parties can see
the uncrustify recommendations if desired, but without preventing the
changes from being merged. This leaves it at the discretion of the
ArmPkg maintainers to decide which level of conformance is required.

Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: "Kinney, Michael D" <michael.d.kinney@intel.com>
Cc: Michael Kubacki <mikuback@linux.microsoft.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>

ArmPkg/ArmPkg.ci.yaml

@@ -239,5 +239,10 @@
         ],
         "AdditionalIncludePaths": [] # Additional paths to spell check
                                      # (wildcards supported)
+    },
+
+    # options defined in .pytool/Plugin/UncrustifyCheck
+    "UncrustifyCheck": {
+        "AuditOnly": True
     }
 }