firmware: qcom_scm-32: Fill SMCCC register in qcom_scm_call

- Move SMCCC register filling to qcom_scm_call so that qcom_scm_call_do
  only needs to concern itself with retry mechanism.
- Use arm_smccc_args struct in atomic variants as well.

Change-Id: I435d974724118943084f618f63fffb1109d1cfe0
Signed-off-by: Elliot Berman <eberman@codeaurora.org>