sim-se add readv and modifies writev

Change-Id: I6cbce4389d5697da34058dc910306394e48c6582
Reviewed-on: https://gem5-review.googlesource.com/c/12117
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>