ARM: dts: imx27-phytec-phycore-som: Move PMIC IRQ GPIO into a separate pin group

The hardware is better described if we place the PMIC IRQ GPIO into its own
pingroup.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>