powerpc/book3e: Add generic 64-bit idle powersave support

We use a similar technique to ppc32: We set a thread local flag
to indicate that we are about to enter or have entered the stop
state, and have fixup code in the async interrupt entry code that
reacts to this flag to make us return to a different location
(sets NIP to LINK in our case).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
--
v2. Fix lockdep bug
    Re-mask interrupts when coming back from idle
diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
index 2bad6e5..adc8e6c 100644
--- a/arch/powerpc/include/asm/machdep.h
+++ b/arch/powerpc/include/asm/machdep.h
@@ -278,6 +278,7 @@
 extern void power4_idle(void);
 extern void power4_cpu_offline_powersave(void);
 extern void ppc6xx_idle(void);
+extern void book3e_idle(void);
 
 /*
  * ppc_md contains a copy of the machine description structure for the