systemc: Use c++11 partial functions instead of boosts.

systemc: Use c++11 partial functions instead of boosts.

This creates a depenendency on c++11 which the headers otherwise avoid,
but gem5 itself already has a c++11 dependency and not a boost
dependency, and outside of having a local copy of boost (which
Accellera does) there isn't a good way to put the placeholder values
_1, _2, etc., into the custom sc_unnammed namespace.

Change-Id: I52ca4c1bc52bef6ff2c62e9f3c32af46f95244dc
Reviewed-on: https://gem5-review.googlesource.com/c/13193
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>