mem-cache,python: Allow custom TLB and events in each prefetcher.
mem-cache,python: Allow custom TLB and events in each prefetcher.

The `BasePrefetcher` python class had members `_events` and `_tlbs`
defined as lists, meaning that any call to `list.append` on them would
affect `_events` and `_tlbs` for all prefetchers, not just the calling
object.  This change redefines them as instance members to fix the
problem.

Change-Id: I68feb1d6d78e2fa5e8775afba8c81c6dd0de6c60
Signed-off-by: Isaac Sánchez Barrera <188c8d979376bf5063d02dc6c7a13a248d20bf36@bsc.es>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32394
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Reviewed-by: Nikos Nikoleris <b6a1b3cd9d36c44e9eeb16bc870df3cb2a0cf469@arm.com>

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