cpu-o3: Add missing vector stat initializers

cpu-o3: Add missing vector stat initializers

All of the O3 vector stats added by 'arch: ISA parser additions of
vector registers' are currently missing their stat initializers. Add
the missing stat initialization to InstructionQueue::regStats.

Change-Id: Idc4b8e2824120a2542d8a604340a1b41bde6aa28
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/6101
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>