Bluetooth: services: Move Heart rate service

This commit moves the BLE GATT heart rate service from
samples/bluetooth/gatt to subsys/bluetooth/services and adds a Kconfig
entry to enable and configure the service.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>

include/bluetooth/services/hrs.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_BLUETOOTH_SERVICES_HRS_H_
+#define ZEPHYR_INCLUDE_BLUETOOTH_SERVICES_HRS_H_
+
+/**
+ * @brief Heart Rate Service (HRS)
+ * @defgroup bt_gatt_hrs Heart Rate Service (HRS)
+ * @ingroup bluetooth
+ * @{
+ *
+ * [Experimental] Users should note that the APIs can change
+ * as a part of ongoing development.
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** @brief Notify heart rate measurement.
+ *
+ * This will send a GATT notification to all current subscribers.
+ *
+ *  @param heartrate The heartrate measuremennt in beats per minute.
+ *
+ *  @return Zero in case of success and error code in case of error.
+ */
+int bt_gatt_hrs_notify(u16_t heartrate);
+
+#ifdef __cplusplus
+}
+#endif
+
+/**
+ * @}
+ */
+
+#endif /* ZEPHYR_INCLUDE_BLUETOOTH_SERVICES_HRS_H_ */