arch-riscv: Ignore sched_yield syscall in SE mode
arch-riscv: Ignore sched_yield syscall in SE mode

Change-Id: I14f22c06eb8fdbe063980b4cd0a49387b9113a97
Reviewed-on: https://gem5-review.googlesource.com/6961
Maintainer: Brandon Potter <0c4047814a967fe28855a3d9d73d9b4959444c57@amd.com>
Reviewed-by: Alec Roelke <8e4f8facd4fb6c7d77135df4850f69a92e6a8660@virginia.edu>

gem5/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,TUD-OS/gem5-dtu,gem5/gem5,TUD-OS/gem5-dtu,gem5/gem5,TUD-OS/gem5-dtu,gem5/gem5,gem5/gem5,TUD-OS/gem5-dtu,gem5/gem5,TUD-OS/gem5-dtu