soc: qcom: smem: Support dynamic item limit

In V12 SMEM, SBL writes SMEM parameter information after the TOC. Use
the SBL provided item count as the max item number.

Signed-off-by: Chris Lew <clew@codeaurora.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>