This adds RISCV boot tests. Due to TODO items highlighted here: https://gem5.atlassian.net/browse/GEM5-1080, these tests only run to a tick as the RISCV disk image does not contain the necessary features to run a proper "boot-exit" test as we do with the X86 boot tests. Change-Id: I0744ff46f78e6ec83b7eabf53146397caad9b97a Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49869 Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu> Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu> Tested-by: kokoro <noreply+kokoro@google.com>