clk: corenet: Adds the clock binding

Adds the clock bindings for Freescale PowerPC CoreNet platforms

Signed-off-by: Tang Yuantian <Yuantian.Tang@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
[scottwood@freescale.com: fixed clock-frequency in example]
Signed-off-by: Scott Wood <scottwood@freescale.com>