mem-cache: Update default prefetch options.

Update the default prefetch options to achieve out-of-the box
prefetcher performance closer to that which a typical user would
expect. Configurations that set these parameters explicitly will be
unaffected.

The new defaults were identified as part of work on gem5 prefetchers
undertaken by Nikolaos Kyparissas while on internship at Arm.

Change-Id: Id63868c7c8f00ee15a0b09a6550780a45ae67e55
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/mem/cache/Cache.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2012-2013, 2015, 2018 ARM Limited
+# Copyright (c) 2012-2013, 2015, 2018, 2022 Arm Limited
 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall
@@ -112,7 +112,7 @@ class BaseCache(ClockedObject):
         "Notify the hardware prefetcher on every access (not just misses)",
     )
     prefetch_on_pf_hit = Param.Bool(
-        False, "Notify the hardware prefetcher on hit on prefetched lines"
+        True, "Notify the hardware prefetcher on hit on prefetched lines"
     )
 
     tags = Param.BaseTags(BaseSetAssoc(), "Tag store")