arch-riscv: Revert change-45522

This reverts change:
https://gem5-review.googlesource.com/c/public/gem5/+/45522.

This reverts commit 1cf41d4c54c988ef4808d8efc1f6212e54a4c120.

Reason for revert:

The above commit caused booting Linux using RISCV either to
hang or to take significantly time more than to finish.

For the v21-1 release, the above commit will be reverted.

JIRA: https://gem5.atlassian.net/browse/GEM5-1043

Change-Id: I58fbe96d7ea50031eba40ff49dabdef971faf6ff
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48099
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>