powerpc/shared: Use static key to detect shared processor

With the static key shared processor available, is_shared_processor()
can return without having to query the lppaca structure.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Phil Auld <pauld@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191213035036.6913-2-mpe@ellerman.id.au

arch/powerpc/include/asm/spinlock.h

@@ -112,13 +112,8 @@ static inline void splpar_rw_yield(arch_rwlock_t *lock) {};
 
 static inline bool is_shared_processor(void)
 {
-/*
- * LPPACA is only available on Pseries so guard anything LPPACA related to
- * allow other platforms (which include this common header) to compile.
- */
-#ifdef CONFIG_PPC_PSERIES
-	return (IS_ENABLED(CONFIG_PPC_SPLPAR) &&
-		lppaca_shared_proc(local_paca->lppaca_ptr));
+#ifdef CONFIG_PPC_SPLPAR
+	return static_branch_unlikely(&shared_processor);
 #else
 	return false;
 #endif