gpu-compute: Cleanup the scheduler a bit

Change-Id: If2c626544f208e15c91be975dee9253126862ced
Reviewed-on: https://gem5-review.googlesource.com/10222
Reviewed-by: Alexandru Duțu <alexandru.dutu@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>

gpu-compute: AMD's baseline GPU model