[AArch64] Exclude optional features from HasV8_0rOps.

The following SubtargetFeatures are removed from the definition of
HasV8_0rOps, on the grounds that they are optional in Armv8.4-A, and
therefore (by the definition of Armv8.0-R) also optional in v8.0-R:

 * performance monitoring: FeaturePerfMon
 * cryptography: FeatureSM4 and FeatureSHA3
 * half-precision FP: FeatureFullFP16, FeatureFP16FML
 * speculation control: FeatureSSBS, FeaturePredRes, FeatureSB,
   FeatureSpecRestrict

This isn't the full set of features that are listed as optional in the
spec. FeatureCCIDX and FeatureTRACEV8_4 are also optional. But LLVM
includes those in HasV8_3aOps and HasV8_4aOps respectively (I think on
the grounds that the system registers they enable are useful to be
able to access after a runtime check), and so for consistency, I've
left those in HasV8_0rOps too.

After this commit, HasV8_0rOps is a strict subset of HasV8_4aOps (but
missing features that are not in Armv8.0-R at all).

The definition of Cortex-R82 is correspondingly updated to add most of
the features that I've removed from base Armv8.0-R (with the exception
of the cryptography ones), since that particular implementation of
v8.0-R does have them.

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D118045

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