firmware/qcom_scm: Add scm call to handle smmu errata

Qcom's smmu-500 needs to toggle wait-for-safe logic to
handle TLB invalidations.
Few firmwares allow doing that through SCM interface.
Add API to toggle wait for safe from firmware through a
SCM call.

Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Ondrej Kubik <ondrej.kubik@canonical.com>