systemc: Merge notify and notifyWork and ignore disabled for resets.

systemc: Merge notify and notifyWork and ignore disabled for resets.

Always notify a process if a reset signal changed, even if it's
disabled. Also, because notify was what checked disabled and only
notifyWork was virtual, this change merges the two so both can be
overridden without any extra virtual functions.

Change-Id: I1e3563fa587aab65a5e95cd8a382ed48e093de3b
Reviewed-on: https://gem5-review.googlesource.com/c/13188
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>