cpu: Rename initiateHtmCmd to be more generic

To prepare for future CHI work, rename ExecContext::initiateHtmCmd to
ExecContext::initiateSpecialMemCmd

JIRA: https://gem5.atlassian.net/browse/GEM5-1097

Change-Id: I7c7aed8ec06a66d9023c14dba37eae42907df222
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56598
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/cpu/simple/exec_context.hh

@@ -446,9 +446,9 @@ class SimpleExecContext : public ExecContext
     }
 
     Fault
-    initiateHtmCmd(Request::Flags flags) override
+    initiateSpecialMemCmd(Request::Flags flags) override
     {
-        return cpu->initiateHtmCmd(flags);
+        return cpu->initiateSpecialMemCmd(flags);
     }
 
     /**