gdb/amd-dbgapi: factor out require_forward_progress overload to target one inferior

A following patch will want to call require_forward_progress for a given
inferior.  Extract a new require_forward_progress overload from the
existing require_forward_progress function that targets a specific
inferior.

Change-Id: I54f42b83eb8443d4d91747ffbc86eaeb017f1e49
Approved-by: Lancelot Six <lancelot.six@amd.com>