ARM64: dts: bcm283x: Use dtsi for USB host mode

In case dr_mode isn't passed via DT, the dwc2 driver defaults
to OTG mode. But the Raspberry Pi 3 is designed only for host mode.
So fix this issue by linking to the dtsi file which set the dr_mode
to host.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>