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>
Change-Id: I38b7c60f5cb81637e6fcc72417e058f8aac09dde
Git-commit: 4d91d7b099508831e82ef209bba71c8b636886a2
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Anant Goel <anantg@codeaurora.org>