mem-ruby: expose transition info to actions

mem-ruby: expose transition info to actions

SLICC compiler generates the curTransitionEvent and
curTransitionNextState functions, which allows actions to check which
event triggered the current transition and what's the next state.

Change-Id: I79c8c4f2839633b7fb3b23cbbdbb32f25db90eab
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31420
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>