secmem: Prepare for easier debugging.

* src/secmem.c (_gcry_secmem_dump_stats): Factor code out to ...
(secmem_dump_stats_internal): new.

This allows to insert call to the dump function during debug sessions
inside of the allocators or call secmem_dump_stats_internal from gdb.

• Signed-off-by: Werner Koch <wk@gnupg.org>