Add a new function, dumper_create(), to allocate a dumper.
dumper_insert() will call this function and retains the existing
behaviour.
This is desirable for performing live dumps of the system. Here, there
is a need to allocate and configure a dumper structure that is invoked
outside of the typical debugger context. Therefore, it should be
excluded from the list of panic-time dumpers.
free_single_dumper() is made public and renamed to dumper_destroy().