perf callchain: Fixup help/config for no-unwinding

perf callchain: Fixup help/config for no-unwinding

Since 841e3558b2d ("perf callchain: Recording 'dwarf' callchains do not
need DWARF unwinding support"), --call-graph dwarf is allowed in 'perf
record' even without unwind support.  A couple of other places don't
reflect this yet though: the help text should list dwarf as a valid
record mode and the dump_size config should be respected too.

Signed-off-by: Rabin Vincent <rabinv@axis.com>
Cc: He Kuang <hekuang@huawei.com>
Fixes: 841e3558b2de ("perf callchain: Recording 'dwarf' callchains do not need DWARF unwinding support")
Link: http://lkml.kernel.org/r/1470837148-7642-1-git-send-email-rabin.vincent@axis.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>