powerpc: add context.vdso_base for 32-bit too

This adds a vdso_base element to the mm_context_t for 32-bit compiles
(both for ARCH=powerpc and ARCH=ppc).  This fixes the compile errors
that have been reported in arch/powerpc/kernel/signal_32.c.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/drivers/macintosh/via-pmu.c b/drivers/macintosh/via-pmu.c
index 0b5ff55..c63d4e7 100644
--- a/drivers/macintosh/via-pmu.c
+++ b/drivers/macintosh/via-pmu.c
@@ -2268,7 +2268,7 @@
  		_set_L2CR(save_l2cr);
 	
 	/* Restore userland MMU context */
-	set_context(current->active_mm->context, current->active_mm->pgd);
+	set_context(current->active_mm->context.id, current->active_mm->pgd);
 
 	/* Power things up */
 	pmu_unlock();
@@ -2366,7 +2366,7 @@
  		_set_L3CR(save_l3cr);
 	
 	/* Restore userland MMU context */
-	set_context(current->active_mm->context, current->active_mm->pgd);
+	set_context(current->active_mm->context.id, current->active_mm->pgd);
 
 	/* Tell PMU we are ready */
 	pmu_unlock();