ARM: dts: imx27-phytec-phycore-som: Add spi-cs-high property to PMIC

Since SPI core does not use GPIO bindings for CS GPIOs,
we should add an active high level declaration.

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