mm: arch: make in_gate_area take an mm_struct instead of a task_struct

Morally, the question of whether an address lies in a gate vma should be asked
with respect to an mm, not a particular task.  Moreover, dropping the dependency
on task_struct will help make existing and future operations on mm's more
flexible and convenient.

Signed-off-by: Stephen Wilson <wilsons@start.ca>
Reviewed-by: Michel Lespinasse <walken@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/powerpc/kernel/vdso.c

@@ -825,7 +825,7 @@ int in_gate_area_no_task(unsigned long addr)
 	return 0;
 }
 
-int in_gate_area(struct task_struct *task, unsigned long addr)
+int in_gate_area(struct mm_struct *mm, unsigned long addr)
 {
 	return 0;
 }