ARM: dts: add usb udc support to bcm281xx

Adds USB OTG/PHY and clock support to BCM281xx and enables
UDC support on the bcm11351-brt and bcm28155-ap boards.

Signed-off-by: Matt Porter <mporter@linaro.org>
Reviewed-by: Markus Mayer <markus.mayer@linaro.org>
Reviewed-by: Tim Kryger <tim.kryger@linaro.org>
Signed-off-by: Christian Daudt <bcm@fixthebug.org>