cpu: Clean up some style issues in pc_event.(hh|cc).

cpu: Clean up some style issues in pc_event.(hh|cc).

The record_t typedef isn't all that helpful, and is also not consistent
with gem5 style. The map_t style is more useful but is also not
compliant. This change eliminates the first typedef and replaces the
second with a type called Map.

There are some other small style fixups added in as well, like making
the member variable pc_map pcMap.

Change-Id: I8ffea529004fd6d5b42fdc60250804e2e4987e88
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21781
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>