ARM: qcom: scm: Add atomic SCM APIs

The atomic SCM APIs are useful for commands that are guaranteed by the
secure side to be uninterruptable, atomic and SMP safe.  The calling
convention use registers for passing parameters and return values between
the secure and non-secure side. Support this interface with
scm_call_atomic[1-2]() functions corresponding to the number of arguments
passed.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kumar Gala <galak@codeaurora.org>