Add SiP (Silicon Provider) services function to issue
SMC call to Arm Trusted Firmware.
More SiP information could be found in
https://github.com/ARM-software/arm-trusted-firmware/blob/master/
docs/arm-sip-service.rst
Signed-off-by: Peng Fan
Reviewed-by: Fabio Estevam
Cc: Stefano Babic