powerpc: Merge time.c and asm/time.h.

We now use the merged time.c for both 32-bit and 64-bit compilation
with ARCH=powerpc, and for ARCH=ppc64, but not for ARCH=ppc32.
This removes setup_default_decr (folds its function into time_init)
and moves wakeup_decrementer into time.c.  This also makes an
asm-powerpc/rtc.h.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/irq.h b/include/asm-powerpc/irq.h
index 980393a..07c2b3f 100644
--- a/include/asm-powerpc/irq.h
+++ b/include/asm-powerpc/irq.h
@@ -496,5 +496,7 @@
 
 #endif /* CONFIG_IRQSTACKS */
 
+extern void do_IRQ(struct pt_regs *regs);
+
 #endif /* _ASM_IRQ_H */
 #endif /* __KERNEL__ */