dt-binding: net: ti: am65x-cpts: add 'ti,pps' property

Add the ti,pps property used to indicate the pair of HWx_TS_PUSH input and
the TS_GENFy output.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>