ARM: dts: am335x: Support the PMIC interrupt

AM335x bone based boards have the PMIC interrupt named NMI which is
connected to TPS65217 device. AM335x main interrupt controller provides it
and the number is 7.

Signed-off-by: Milo Kim <woogyom.kim@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>