soc: qcom: smem: Update max processor count

Update max processor count to reflect the number of
co-processors on SC7180 SoCs.

Reviewed-by: Vinod Koul <vkoul@kernel.org>
Tested-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>