mem-cache: Add a mechanism to iterate all entries of an AssociativeSet
mem-cache: Add a mechanism to iterate all entries of an AssociativeSet

Added functions to obtain an iterator to access all entries of
an AssociativeSet container.

Change-Id: I1ec555bd97d97e3edaced2b8f61287e922279c26
Reviewed-on: https://gem5-review.googlesource.com/c/16582
Reviewed-by: Daniel Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>
Reviewed-by: Nikos Nikoleris <b6a1b3cd9d36c44e9eeb16bc870df3cb2a0cf469@arm.com>
Maintainer: Nikos Nikoleris <b6a1b3cd9d36c44e9eeb16bc870df3cb2a0cf469@arm.com>

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