dt-bindings: arm: bcm: add BCM53573 SoCs family binding

BCM53573 is a family derived from Northstar with some important
differences:
1. Cortex-A9 replaced by Cortex-A7
2. XHCI controller dropped
3. Two Ethernet interfaces removed
4. Two 802.11ac cores embedded

Linux already contains DTS files for some on those devices so add a
proper binding for it.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230710175944.32631-1-zajec5@gmail.com


Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>