soc: qcom: smem: Update max processor count

Update max processor count to reflect the number of co-processors on
SC7280 SoCs.

Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Link: https://lore.kernel.org/r/1615269111-25559-2-git-send-email-sibis@codeaurora.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>