mips: dts: brcm: bcm7435: add "interrupt-names" for NAND controller

Second interrupt can be DMA or EDU one. Specify it explicitly using
interrupt-names property. This matches documented binding.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>