powerpc: Implement task_pt_regs() accessor

The task_pt_regs() macro allows access to the pt_regs of a given task.

This macro is not currently defined for the powerpc architecture, but
we need it for some upcoming utrace additions.

Signed-off-by: Srinivasa DS <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

include/asm-powerpc/processor.h

···
 #define thread_saved_pc(tsk)    \
         ((tsk)->thread.regs? (tsk)->thread.regs->nip: 0)
 
+#define task_pt_regs(tsk)	((struct pt_regs *)(tsk)->thread.regs)
+
 unsigned long get_wchan(struct task_struct *p);
 
 #define KSTK_EIP(tsk)  ((tsk)->thread.regs? (tsk)->thread.regs->nip: 0)