powerpc/mm/hash: Abstract context id allocation for KVM

KVM wants to be able to allocate an MMU context id, which it does
currently by calling __init_new_context().

We're about to rework that code, so provide a wrapper for KVM so it
can not worry about the details.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
index 73bf6e1..650a498 100644
--- a/arch/powerpc/mm/mmu_context_book3s64.c
+++ b/arch/powerpc/mm/mmu_context_book3s64.c
@@ -30,7 +30,7 @@
 static DEFINE_SPINLOCK(mmu_context_lock);
 static DEFINE_IDA(mmu_context_ida);
 
-int __init_new_context(void)
+static int __init_new_context(void)
 {
 	int index;
 	int err;
@@ -57,7 +57,13 @@ int __init_new_context(void)
 
 	return index;
 }
-EXPORT_SYMBOL_GPL(__init_new_context);
+
+int hash__alloc_context_id(void)
+{
+	return __init_new_context();
+}
+EXPORT_SYMBOL_GPL(hash__alloc_context_id);
+
 static int radix__init_new_context(struct mm_struct *mm, int index)
 {
 	unsigned long rts_field;