Add a header for the SIP interface defined to access the dcf controller
handling ddr rate changes on rk3399 (and most likely later socs).
This interface is shared between the clock driver as well as the
The SIP interface counterpart was merged from pull-request #684 
into the upstream arm-trusted-firmware codebase.
 https://github.com/ARM-software/arm-trusted-firmware/pull/684Signed-off-by: Lin Huang <firstname.lastname@example.org>
Signed-off-by: Heiko Stuebner <email@example.com>