mm: provide init_mm mm_context initializer

Provide an INIT_MM_CONTEXT intializer macro which can be used to
statically initialize mm_struct:mm_context of init_mm.  This way we can
get rid of code which will do the initialization at run time (on s390).

In addition the current code can be found at a place where it is not
expected.  So let's have a common initializer which architectures
can use if needed.

This is based on a patch from Suzuki Poulose.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Suzuki Poulose <suzuki@in.ibm.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/init-mm.c b/mm/init-mm.c
index 57aba0d..1d29cdf 100644
--- a/mm/init-mm.c
+++ b/mm/init-mm.c
@@ -7,6 +7,11 @@
 
 #include <asm/atomic.h>
 #include <asm/pgtable.h>
+#include <asm/mmu.h>
+
+#ifndef INIT_MM_CONTEXT
+#define INIT_MM_CONTEXT(name)
+#endif
 
 struct mm_struct init_mm = {
 	.mm_rb		= RB_ROOT,
@@ -17,4 +22,5 @@
 	.page_table_lock =  __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
 	.mmlist		= LIST_HEAD_INIT(init_mm.mmlist),
 	.cpu_vm_mask	= CPU_MASK_ALL,
+	INIT_MM_CONTEXT(init_mm)
 };