ARM: dts: imx27-phytec-phycore-som: Rename file to .dtsi

PCM-038 module cannot be used standalone. This patch renames
module file to .dtsi and excludes it from compilation.

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