net: ethernet: ti: icss-iep: Add support for IEP on AM335x platforms

ICSS IEP on AM335x does not support any of the following features:
- 64 Bit counter
- SLOW compensation
- Shadow mode
Also reg map is not compatible with either of AM57xx and AM65x.
So add an AM335x specific compatible to capture all these differences.

Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>