firmware: qcom: scm: Expose secure IO service

The secure IO service provides operations for reading and writing secure
memory from non-secure mode, expose this API through SCM.

Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>