soc: qcom: rmtfs-mem: Validate that scm is available

commit 137dc5843faeacabf48fc22a8dc58c4e0b4f0927 upstream.

The scm device must be present in order for the rmtfs driver to
configure memory permissions for the rmtfs memory region, so check that
it is probed before continuing.

Cc: stable@vger.kernel.org
Fixes: fa65f804 ("soc: qcom: rmtfs-mem: Add support for assigning memory to remote")
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>