greybus: battery: use feature tag rather than kernel version

Conditionally define a new symbol DRIVER_OWNS_PSY_STRUCT, which is
set in "kernel_ver.h" based on on the kernel version.  Use it to
distinguish code used for kernels that differ in whether a power
supply structure is owned by the driver, or by the power supply
core.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/battery.c

@@ -7,7 +7,6 @@
  * Released under the GPLv2 only.
  */
 
-#include <linux/version.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/slab.h>
@@ -20,7 +19,7 @@ struct gb_battery {
 	 * and new apis in the same driver for now, until this is merged
 	 * upstream, when all of these version checks can be removed.
 	 */
-#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 1, 0)
+#ifdef DRIVER_OWNS_PSY_STRUCT
 	struct power_supply bat;
 #define to_gb_battery(x) container_of(x, struct gb_battery, bat)
 #else
@@ -295,7 +294,7 @@ static enum power_supply_property battery_props[] = {
 	POWER_SUPPLY_PROP_VOLTAGE_NOW,
 };
 
-#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 1, 0)
+#ifdef DRIVER_OWNS_PSY_STRUCT
 static int init_and_register(struct gb_connection *connection,
 			     struct gb_battery *gb)
 {
@@ -362,7 +361,7 @@ static void gb_battery_connection_exit(struct gb_connection *connection)
 {
 	struct gb_battery *gb = connection->private;
 
-#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 1, 0)
+#ifdef DRIVER_OWNS_PSY_STRUCT
 	power_supply_unregister(&gb->bat);
 #else
 	power_supply_unregister(gb->bat);

drivers/staging/greybus/kernel_ver.h

@@ -15,6 +15,12 @@
 #define __GREYBUS_KERNEL_VER_H
 
 #include <linux/kernel.h>
+#include <linux/version.h>
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 1, 0)
+/* Commit: 297d716 power_supply: Change ownership from driver to core */
+#define DRIVER_OWNS_PSY_STRUCT
+#endif
 
 #ifndef __ATTR_WO
 #define __ATTR_WO(_name) {						\
@@ -57,7 +63,6 @@
  * 3.17, which they explicitly changed in the 3.17 kernel.  Consistency is
  * overrated.
  */
-#include <linux/version.h>
 #include <linux/gpio.h>
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 17, 0)