rpmsg: Allow RPMSG_VIRTIO to be enabled via menuconfig or defconfig

Currently, RPMSG_VIRTIO can only be enabled if some other kconfig
option selects it. This does not allow it to be enabled for
virtualized systems where Virtio RPMSG is available over Virtio
MMIO or PCI transport.

This patch updates RPMSG_VIRTIO kconfig option so that we can
enable the VirtIO RPMSG driver via menuconfig or defconfig. The
patch also removes "select RPMSG_VIRTIO" from various remoteproc
kconfig options because it is now user selectable.
Signed-off-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/Kconfig

@@ -28,7 +28,6 @@ config OMAP_REMOTEPROC
 	depends on OMAP_IOMMU
 	select MAILBOX
 	select OMAP2PLUS_MBOX
-	select RPMSG_VIRTIO
 	help
 	  Say y here to support OMAP's remote processors (dual M3
 	  and DSP on OMAP4) via the remote processor framework.
@@ -58,7 +57,6 @@ config DA8XX_REMOTEPROC
 	tristate "DA8xx/OMAP-L13x remoteproc support"
 	depends on ARCH_DAVINCI_DA8XX
 	depends on DMA_CMA
-	select RPMSG_VIRTIO
 	help
 	  Say y here to support DA8xx/OMAP-L13x remote processors via the
 	  remote processor framework.
@@ -79,7 +77,6 @@ config DA8XX_REMOTEPROC
 config KEYSTONE_REMOTEPROC
 	tristate "Keystone Remoteproc support"
 	depends on ARCH_KEYSTONE
-	select RPMSG_VIRTIO
 	help
 	  Say Y here here to support Keystone remote processors (DSP)
 	  via the remote processor framework.
@@ -135,7 +132,6 @@ config ST_REMOTEPROC
 	depends on ARCH_STI
 	select MAILBOX
 	select STI_MBOX
-	select RPMSG_VIRTIO
 	help
 	  Say y here to support ST's adjunct processors via the remote
 	  processor framework.

drivers/rpmsg/Kconfig

@@ -47,7 +47,8 @@ config RPMSG_QCOM_SMD
 	  platforms.
 
 config RPMSG_VIRTIO
-	tristate
+	tristate "Virtio RPMSG bus driver"
+	depends on HAS_DMA
 	select RPMSG
 	select VIRTIO