Documentation/arm64/sve: Couple of improvements and typos

  - Fix mismatch between SVE registers (Z) and FPSIMD register (V)
  - Don't prefix the path for [3] with Linux to stay consistent with
    [1] and [2].

Signed-off-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>