mem-ruby: Deep renaming of Prefetcher to RubyPrefetcher

mem-ruby: Deep renaming of Prefetcher to RubyPrefetcher

A recent change (https://gem5-review.googlesource.com/c/
public/gem5/+/27949) updated the ruby prefetcher name,
which breaks the use of old name in some SLICC files.
This change makes sure that the new name is used at all
places.

Issue-On: https://gem5.atlassian.net/browse/GEM5-498
Change-Id: Ic667b61eac13dc7c267cee7dce3aa970f7ae9a8b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28667
Reviewed-by: Timothy Hayes <timothy.hayes@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>