TEMP: dt-bindings: soc: ti: pruss: Add IEP and CORE clock mux

ICSS/ICSSG modules have an IEP clock mux that allow selection
of internal IEP clock from 2 clock sources.

ICSSG module has a CORE clock mux that allows selection
of internal CORE clock from 2 clock sources.

Add binding information for these 2 clock muxes.

Signed-off-by: Roger Quadros <rogerq@ti.com>
[s-anna@ti.com: few minor fixups]
Signed-off-by: Suman Anna <s-anna@ti.com>