firmware: qcom: scm: Use atomic SCM for cold boot

This patch changes the cold_set_boot_addr function to use atomic SCM
calls.  cold_set_boot_addr required adding qcom_scm_call_atomic2 to
support the two arguments going to the smc call.  Using atomic removes
the need for memory allocation and instead places all arguments in
registers.

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