sched/headers: Move task->mm coredumping related defines and methods from <linux/sched.h> to <linux/sched/coredump.h>

This further reduces the size and complexity of <linux/sched.h>.

These are the definitions and APIs that are moved:

  # MMF_*:
  fs/binfmt_elf.c
  fs/binfmt_elf_fdpic.c
  fs/exec.c
  fs/proc/base.c
  include/linux/khugepaged.h
  include/linux/ksm.h
  include/linux/sched/coredump.h
  kernel/events/uprobes.c
  kernel/fork.c
  mm/huge_memory.c
  mm/khugepaged.c
  mm/ksm.c
  mm/memory.c
  mm/oom_kill.c

  # SUID_DUMP_*:
  arch/ia64/include/asm/processor.h
  fs/coredump.c
  fs/exec.c
  fs/proc/internal.h
  include/linux/sched/coredump.h
  kernel/ptrace.c
  kernel/sys.c
  kernel/sysctl.c

  # get_dumpable():
  arch/ia64/include/asm/processor.h
  fs/coredump.c
  fs/exec.c
  fs/proc/internal.h
  include/linux/sched/coredump.h
  kernel/ptrace.c
  kernel/sys.c

  # set_dumpable():
  fs/exec.c
  include/linux/sched/coredump.h
  kernel/cred.c
  kernel/sys.c
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>