ARM: dts: imx27-phytec-phycore-som: Enable SSI1

This patch adds pin group for Synchronous Serial Interface 1 (SSI1)
for PCM-038 module and enables this interface. This change do nothing
at the current stage but helps to continue develop sound support.

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