remoteproc: qcom: Loosen dependency on RPMSG_QCOM_SMD

There doesn't seem to be any actual build time dependency on the
RPMSG_QCOM_SMD, besides that these drivers should be a module if the smd
rpmsg code is a module. Drop the compile test dependency so that these
drivers can be used without RPMSG_QCOM_SMD being enabled. This is useful
for the qcom SoCs that are using RPMSG_QCOM_GLINK_SMEM instead of
RPMSG_QCOM_SMD and thus don't want to enable the SMD driver when it is
never used.

Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20210823235120.1203512-2-swboyd@chromium.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>