sysfs.h: add __ATTR_RW() macro

A number of parts of the kernel created their own version of this, might
as well have the sysfs core provide it instead.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/sysfs.h

@@ -79,6 +79,8 @@ struct attribute_group {
 	.show	= _name##_show,					\
 }
 
+#define __ATTR_RW(_name) __ATTR(_name, 0644, _name##_show, _name##_store)
+
 #define __ATTR_NULL { .attr = { .name = NULL } }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC