score: Fix implicit includes now failing build after extable change

After changing from module.h to extable.h, score builds fail with:

  arch/score/kernel/traps.c: In function 'do_ri':
  arch/score/kernel/traps.c:248:4: error: implicit declaration of function 'user_disable_single_step'
  arch/score/mm/extable.c: In function 'fixup_exception':
  arch/score/mm/extable.c:32:38: error: dereferencing pointer to incomplete type
  arch/score/mm/extable.c:34:24: error: dereferencing pointer to incomplete type

because extable.h doesn't drag in the same amount of headers as the
module.h did.  Add in the headers which were implicitly expected.

Fixes: 90858794 ("module.h: remove extable.h include now users have migrated")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
[PG: tweak commit log; refresh for sched header refactoring.]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>