ARM: dts: bcm283x: Add dtsi for USB host mode

In case dr_mode isn't passed via DT, the dwc2 defaults to OTG mode.
But all Raspberry Pi boards here are designed only for host mode.
So fix this issue by providing a dtsi file which set the dr_mode
to host.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Eric Anholt <eric@anholt.net>