DynamicTablesPkg: Exempt some _CPC field from checks

When generating _CPC objects, some fields are mandatory by spec [1].
Some fields cannot be supported by a the Juno platform, which is used
to test the _CPC generation. Therefore, rely on the
PcdDevelopmentPlatformRelaxations Pcd to either:
- warn about the missing fields and and let the OS handle the
  missing information
- consider the missing fields as an error

_CPC fields that are exempted from checks when the Pcd is set:
- PerformanceLimitedRegister
- ReferencePerformanceCounterRegister
- DeliveredPerformanceCounterRegister

[1] Cf. non-optional fields in:
    ACPI 6.5, s8.4.6.1 '_CPC (Continuous Performance Control)'

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

DynamicTablesPkg/Library/Common/AmlLib/AmlLib.inf

@@ -71,6 +71,9 @@
   BaseLib
   MemoryAllocationLib
 
+[FixedPcd]
+  gEdkiiDynamicTablesPkgTokenSpaceGuid.PcdDevelopmentPlatformRelaxations
+
 [BuildOptions]
   *_*_*_CC_FLAGS = -DAML_HANDLE