dt-bindings: soc: ti: pruss: Update bindings for K3 AM65x & J721E SoCs

The K3 AM65x and J721E SoCs have the next generation of the PRU-ICSS IP,
commonly called ICSSG. The ICSSG IP on K3 SoCs has couple of additional
sub-modules (two IEP and MII_RT sub-modules each vs one, a new MII_G_RT
sub-module) w.r.t previous generation PRU-ICSS IPs.

The K3 J721E SoCs have a revised version of the ICSSG IP present on
AM65x. One of the chief differences is the presence of an additional
PRU core per slice called a Tx_PRU, while retaining almost all of the
sub-modules from AM65x.

Update the PRUSS bindings for these newer ICSSG instances including the
info for MII_G_RT.

Signed-off-by: Suman Anna <s-anna@ti.com>