ARM: dts: imx27-phytec-phycore-som: Add initial support for PCM970 RDK

Patch adds initial dts for Phytec PCM970 Rapid development kit.
- Added definition for UART0 and UART1.
- Added additional SPI chipselect which used on RDK for ZegBee module.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>