firmware: arm_scmi: Fix virtio transport Kconfig dependency

ARM_SCMI_TRANSPORT_VIRTIO is a 'bool' Kconfig used to include support for
the SCMI virtio transport inside the core SCMI stack; a bare transport
dependency attached here to this option, though, cannot be properly
propagated to the parent ARM_SCMI_PROTOCOL option and, as a result, it is
currently possible to configure a Kernel where SCMI core is builtin
and includes support for virtio while VirtIO core is =m.
This allowed combination breaks linking:

	ARM_SCMI_PROTOCOL=y
	ARM_SCMI_TRANSPORT_VIRTIO=y
	VIRTIO=m

Bind the dependency in ARM_SCMI_TRANSPORT_VIRTIO to the chosen kind of
compilation of ARM_SCMI_PROTOCOL.

Link: https://lore.kernel.org/r/20210816141609.41751-1-cristian.marussi@arm.com


Fixes: 46abe13b ("firmware: arm_scmi: Add virtio transport")
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Arnd Bergmann <arnd@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>