dsp: add voice MHI driver

Add voice MHI driver to support the following features -
1. Allocate and map mailbox memory needed for voice call
packet exchange.
2. Send memory mapped addresses to ADSP.
3. Vote MHI host driver at start and stop of a voice call.

Change-Id: I8ef8bc270acacab9b80bca7addccdf73bd572adf
Signed-off-by: Vikram Panduranga <vpandura@codeaurora.org>

dsp/q6_init.h

@@ -1,7 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
- * Copyright (c) 2017-2018, The Linux Foundation. All rights reserved.
-*/
+ * Copyright (c) 2017-2019, The Linux Foundation. All rights reserved.
+ */
 
 #ifndef __Q6_INIT_H__
 #define __Q6_INIT_H__
@@ -54,5 +54,19 @@ static inline void audio_slimslave_exit(void)
 {
 };
 #endif
+#ifdef CONFIG_VOICE_MHI
+int voice_mhi_init(void);
+void voice_mhi_exit(void);
+#else
+static inline int voice_mhi_init(void)
+{
+	return 0;
+}
+
+static inline void voice_mhi_exit(void)
+{
+	return;
+}
+#endif
 #endif