ARM: AM33xx: Add support for Clock Synthesizer

ARM: AM33xx: Add support for Clock Synthesizer

The CDCE913 and CDCEL913 devices are modular PLL-based, low cost,
high performance , programmable clock synthesizers. They generate
upto 3 output clocks from a single input frequency. Each output can
be programmed for any clock-frequency.

Adding support for the same.

Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>