ARM: dts: imx27-phytec-phycore-rdk: Add USBH2 node

This patch adds USBH2 devicetree node of Phytec PCM970 RDK.
Additionally, adds fixed regulator to provide functionality
without dummy-regulator in the kernel.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>