cpu: Add VecElem entries in MinorCPU Scoreboard

cpu: Add VecElem entries in MinorCPU Scoreboard

This patch is:
* Increasing the number of bits in the Scoreboard so that
  it is keeping track of VecElemClass dependencies.
* Fixing VecElemClass entry in the scoreboard table so that it
  correctly uses flatIndex rather than index.

Change-Id: Ie4877e5fe410b1437447adebbe289602a443f7c0
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15597
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>