powerpc/process: Replace an #ifdef CONFIG_PPC_47x by IS_ENABLED()

isync() is always defined, no need for an #ifdef.

Replace it by IS_ENABLED(CONFIG_PPC_47x).
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ac8da0e3baa91dda805e1e492fd65aecd90c1fb5.1597643156.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/process.c

@@ -831,9 +831,8 @@ static void switch_hw_breakpoint(struct task_struct *new)
 static inline int __set_dabr(unsigned long dabr, unsigned long dabrx)
 {
 	mtspr(SPRN_DAC1, dabr);
-#ifdef CONFIG_PPC_47x
-	isync();
-#endif
+	if (IS_ENABLED(CONFIG_PPC_47x))
+		isync();
 	return 0;
 }
 #elif defined(CONFIG_PPC_BOOK3S)