ARM: dts: msm: Add KS8851 IRQ pin definition for 8992

Add the pinctrl entry needed to configure the GPIO used as
the IRQ line for the KS8851 SPI Ethernet controller on the
MSM8992 Rumi platform.

Change-Id: I6819f6bf55518e118a53ba46d8fff980d659d47a
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>