ARM: cpuidle: Avoid orphan section warning

Since commit 83109d5d5f ("x86/build: Warn on orphan section placement"),
we get a warning for objects in orphan sections. The cpuidle implementation
for OMAP causes this when CONFIG_CPU_IDLE is disabled:

arm-linux-gnueabi-ld: warning: orphan section `__cpuidle_method_of_table' from `arch/arm/mach-omap2/pm33xx-core.o' being placed in section `__cpuidle_method_of_table'
arm-linux-gnueabi-ld: warning: orphan section `__cpuidle_method_of_table' from `arch/arm/mach-omap2/pm33xx-core.o' being placed in section `__cpuidle_method_of_table'
arm-linux-gnueabi-ld: warning: orphan section `__cpuidle_method_of_table' from `arch/arm/mach-omap2/pm33xx-core.o' being placed in section `__cpuidle_method_of_table'

Change the definition of CPUIDLE_METHOD_OF_DECLARE() to silently
drop the table and all code referenced from it when CONFIG_CPU_IDLE
is disabled.

Fixes: 06ee7a950b ("ARM: OMAP2+: pm33xx-core: Add cpuidle_ops for am335x/am437x")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201230155506.1085689-1-arnd@kernel.org

arch/arm/include/asm/cpuidle.h

@@ -7,9 +7,11 @@
 #ifdef CONFIG_CPU_IDLE
 extern int arm_cpuidle_simple_enter(struct cpuidle_device *dev,
 		struct cpuidle_driver *drv, int index);
+#define __cpuidle_method_section __used __section("__cpuidle_method_of_table")
 #else
 static inline int arm_cpuidle_simple_enter(struct cpuidle_device *dev,
 		struct cpuidle_driver *drv, int index) { return -ENODEV; }
+#define __cpuidle_method_section __maybe_unused /* drop silently */
 #endif
 
 /* Common ARM WFI state */
@@ -42,8 +44,7 @@ struct of_cpuidle_method {
 
 #define CPUIDLE_METHOD_OF_DECLARE(name, _method, _ops)			\
 	static const struct of_cpuidle_method __cpuidle_method_of_table_##name \
-	__used __section("__cpuidle_method_of_table")			\
-	= { .method = _method, .ops = _ops }
+	__cpuidle_method_section = { .method = _method, .ops = _ops }
 
 extern int arm_cpuidle_suspend(int index);