ARM: dts: keystone-k2g: Update the PRUSS IEP nodes

Update the compatible for all PRU-ICSS IEP nodes to ti,am5728-icss-iep,
so that icss_iep driver can be probed. Also add the required clocks
property to IEP nodes.

Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[s-anna@ti.com: update iep clocks]
Signed-off-by: Suman Anna <s-anna@ti.com>