KVM: arm64: Move vcpu configuration flags into their own set

The KVM_ARM64_{GUEST_HAS_SVE,VCPU_SVE_FINALIZED,GUEST_HAS_PTRAUTH}
flags are purely configuration flags. Once set, they are never cleared,
but evaluated all over the code base.

Move these three flags into the configuration set in one go, using
the new accessors, and take this opportunity to drop the KVM_ARM64_
prefix which doesn't provide any help.

Reviewed-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>