rpmsg: qcom_smd: Promote to arch_initcall

qcom_smd's only child, smd-rpm uses arch_initcall and both have to be up
before almost anything else to ensure the MSM SoCs will work fine and
nothing will have to resort to probe defering, as this is the main pillar
of all things DVFS on these machines. Promote it to arch_initcall to avoid
such issues.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211230023253.1123142-1-konrad.dybcio@somainline.org