rpmsg: Introduce Qualcomm SMD backend

This introduces a new rpmsg backend for the Qualcomm SMD system,
allowing communication with various remote processors found in Qualcomm
platforms. The implementation is based on, and intends to replace,
drivers/soc/qcom/smd.c with the necessary adaptions for fitting with the
rpmsg core.

Based on original work by Sricharan R <sricharan@codeaurora.org>

Cc: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/Kconfig

@@ -4,6 +4,16 @@ menu "Rpmsg drivers"
 config RPMSG
 	tristate
 
+config RPMSG_QCOM_SMD
+	tristate "Qualcomm Shared Memory Driver (SMD)"
+	depends on QCOM_SMEM
+	depends on !QCOM_SMD
+	select RPMSG
+	help
+	  Say y here to enable support for the Qualcomm Shared Memory Driver
+	  providing communication channels to remote processors in Qualcomm
+	  platforms.
+
 config RPMSG_VIRTIO
 	tristate
 	select RPMSG

drivers/rpmsg/Makefile

@@ -1,2 +1,3 @@
 obj-$(CONFIG_RPMSG)		+= rpmsg_core.o
+obj-$(CONFIG_RPMSG_QCOM_SMD)	+= qcom_smd.o
 obj-$(CONFIG_RPMSG_VIRTIO)	+= virtio_rpmsg_bus.o