fastmodel: Set simulation pause when breakpoint hit
fastmodel: Set simulation pause when breakpoint hit

The 7th parameter of breakpoint_set_code is dontStop. It seems the
fastmodel would prefetch something or do some evaluation ahead with the
flag set. This behavior prevents the instruction stepping feature of
gdb. The implementation of the feature is creating a breakpoint on the
next instruction and contining the simulation. Without stopping on the
breakpoint, it wouldn't invoke the breakpoint callback, since it may
evaulate the code we just want it to stop already. We should set the
dontStop to false to fix this issue.

Change-Id: Iaf8acd3235fa9625c1423ef34606e1fa5d0c531a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55484
Reviewed-by: Earl Ou <82591a79653dd29c9ce06ea2b578447596bef9ab@google.com>
Reviewed-by: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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