dt-bindings: net: renesas,etheravb: Document RZ/V2M SoC

Document the Ethernet AVB IP found on RZ/V2M SoC.
It includes the Ethernet controller (E-MAC) and Dedicated Direct memory
access controller (DMAC) for transferring transmitted Ethernet frames
to and received Ethernet frames from respective storage areas in the
RAM at high speed.
The AVB-DMAC is compliant with IEEE 802.1BA, IEEE 802.1AS timing and
synchronization protocol, IEEE 802.1Qav real-time transfer, and the
IEEE 802.1Qat stream reservation protocol.

R-Car has a pair of combined interrupt lines:
 ch22 = Line0_DiA | Line1_A | Line2_A
 ch23 = Line0_DiB | Line1_B | Line2_B
Line0 for descriptor interrupts (which we call dia and dib).
Line1 for error related interrupts (which we call err_a and err_b).
Line2 for management and gPTP related interrupts (mgmt_a and mgmt_b).

RZ/V2M hardware has separate interrupt lines for each of these.

It has 3 clocks; the main AXI clock, the AMBA CHI (Coherent Hub
Interface) clock and a gPTP reference clock.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>