ARM: dts: imx27-phytec-phycore-som: Remove UART definitions

UART1 and UART2 can be unused on some designs with PCM038 module.
Remove these definitions from basic dts and lets choose user only
necessary UARTs in custom designs.
Keep UART0 for using this one as boot console, but since we have
not way to disable usage RTSCTS signals, remove this parameter for UART0.

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>