coredump: move core dump functionality into its own file

coredump: move core dump functionality into its own file

This prepares for making core dump functionality optional.

The variable "suid_dumpable" and associated functions are left in fs/exec.c
because they're used elsewhere, such as in ptrace.

Signed-off-by: Alex Kelly <[email protected]>
Reviewed-by: Josh Triplett <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Acked-by: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Al Viro <[email protected]>