systemc: Add an sc_event_finder::find_event method.
systemc: Add an sc_event_finder::find_event method.

The guts of sc_event_finder are supposed to be implementation defined,
but the tests reach in and call this particular method on that class.

Change-Id: I21c18fa68ccce7bc1a13122ee3b452ecb81b713a
Reviewed-on: https://gem5-review.googlesource.com/11274
Reviewed-by: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@google.com>
Maintainer: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@google.com>

gem5/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,gem5/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,gem5/gem5,TUD-OS/gem5-dtu,gem5/gem5,gem5/gem5