tests: Fix riscv boot exit tests
tests: Fix riscv boot exit tests

Due to this change:
https://gem5-review.googlesource.com/c/public/gem5/+/52089
full RISCV boot tests were added, which makes the "tick_exit" parameter
optional (left to 'None' if simulating a full boot). However, the
simulation function was not updated to not pass the "tick_exit"
parameter if not set. This cause an error. This patch fixes this.

Change-Id: I9c62a6a46d9334a2e9fbad2221b42a1ff4843a54
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52644
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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