arm64: dts: ti: k3-am64-main: Add PRU system events for virtio

arm64: dts: ti: k3-am64-main: Add PRU system events for virtio

PRU system events "vring" have been added to each PRU and RTU node
in each of the ICSSG0 and ICSSG1 remote processor subsystems to
enable the virtio/rpmsg communication between MPU and that PRU/RTU core.
No events have been added to the Tx_PRU cores at present. The
additions are done in the base k3-am64main.dtsi, and so are inherited
by all the K3 AM64x boards.

The PRU system events is the preferred approach over using TI
mailboxes, as it eliminates an external peripheral access from
the PRU/RTU-side, and keeps the interrupt generation internal to
the ICSSG. The difference from MPU would be minimal in using one
versus the other.

Mailboxes can still be used if desired, but currently there is
no support on firmware-side for K3 SoCs to use mailboxes. Either
approach would require that an appropriate firmware image is
loaded/booted on the PRU.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Link: https://lore.kernel.org/r/20240529064420.571615-2-danishanwar@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>