arch-riscv: initialize RISC-V's thread pointer register in clone syscall
arch-riscv: initialize RISC-V's thread pointer register in clone syscall

This patch initializes thread pointer register to Thread Local Storage
(TLS)'s pointer given to a clone system call.

Change-Id: I03e2cf4763e6a0ed31f357772a513a05e1e3461b
Reviewed-on: https://gem5-review.googlesource.com/c/9622
Reviewed-by: Brandon Potter <0c4047814a967fe28855a3d9d73d9b4959444c57@amd.com>
Maintainer: Brandon Potter <0c4047814a967fe28855a3d9d73d9b4959444c57@amd.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5