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/Kbuild

@@ -124,6 +124,10 @@ ifdef CONFIG_MSM_MDF
 	Q6_OBJS += msm_mdf.o
 endif
 
+ifdef CONFIG_VOICE_MHI
+	Q6_OBJS += voice_mhi.o
+endif
+
 LINUX_INC +=	-Iinclude/linux
 
 INCS +=		$(COMMON_INC) \