dt-binding: ti: am65x: document common platform time sync cpts module

Document device tree bindings for TI AM654/J721E SoC The Common Platform
Time Sync (CPTS) module. The CPTS module is used to facilitate host control
of time sync operations. Main features of CPTS module are:
  - selection of multiple external clock sources
  - 64-bit timestamp mode in ns with ppm and nudge adjustment.
  - control of time sync events via interrupt or polling
  - hardware timestamp of ext. events (HWx_TS_PUSH)
  - periodic generator function outputs (TS_GENFx)
  - PPS in combination with timesync router
  - Depending on integration it enables compliance with the IEEE 1588-2008
standard for a precision clock synchronization protocol, Ethernet Enhanced
Scheduled Traffic Operations (CPTS_ESTFn) and PCIe Subsystem Precision Time
Measurement (PTM).

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>