Bluetooth: controller: Prepare to introduce LL split architecture

Preparation to introduce the Upper Link Layer (ULL) and
Lower Link Layer (LLL) split architecture.

- Move SoC dependent HAL to vendor specific folder.
- Preparation to split data structures into ULL and LLL
  types.
- Added more role and state conditional compilations.
- Added some work-in-progress implementation of advertising
  extensions, will be used as inspiration in the new split
  architecture work.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

subsys/bluetooth/controller/ll_sw/lll_conn.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2018 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+struct node_tx {
+	union {
+		void        *next;
+		memq_link_t *link;
+	};
+
+	u8_t pdu[];
+};