ARM: dts: BCM53573: Add DT for Luxul XAP-1440

This is BCM53573 WiSoC based outdoor access point with an extra BCM43217
chipset used for 2.4 GHz.

Signed-off-by: Dan Haab <dhaab@luxul.com>
Acked-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>