[AArch64] Fix AArch64TargetParser.def to match AArch64.td.

Currently, we have two different lists of features each CPU supports...
and those lists aren't consistent. This patch assumes AArch64.td is
right, and tries to fix AArch64TargetParser to match.

It's hard to find documentation for the right features, but reviewers
have confirmed these changes.

Probably we should try to unify the two lists at some point, but
synchronizing them seems like a prerequisite to that anyway.

Differential Revision: https://reviews.llvm.org/D122274