Documentation: dt: Add TI SCI clock driver

Add a clock implementation, TI SCI clock, that will hook to the common
clock framework, and allow each clock to be controlled via TI SCI
protocol.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>