[xhci-tegra] Kernel 5.7 regression - tegra124-nyan

Hello!

Since kernel 5.7 (specifically commits 
f67213cee2b35fe169a723746b7f37debf20fa29) the xhci-tegra driver fails to 
initialize the USB ports of tegra124-nyan devices with the message 
"usb-role-switch not found for otg".

The named commit, which adds usb-role-switch support, effectively broke 
all device trees with "otg" or "peripheral" modes that do not include 
the "usb-role-switch" property.

Given that the otg port of nyan devices is just a type A connector, I 
can patch the device tree to use the "host" mode and it works fine, but 
since it seems to be an otg port internally, maybe it's better to add 
the usb-role-switch property with a "connector" subnode.
However, I don't know if other devices are affected, so I think the 
driver should be "fixed" to work again with DTs without usb-role-switch.

Cheers,
Matías Zúñiga