kern,arch: Refactor SkipFuncEvent to not use skipFunction.

kern,arch: Refactor SkipFuncEvent to not use skipFunction.

Replace it with a new virtual function.

Change-Id: I9d516d21ab3b1d1d70ea1297f984f868d3e7c3fb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24111
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>