MIPS: generic: Allow generating FIT image for Marduk board

Marduk is based on IMG pistachio SoC. The platform is using
MIPS UHI booting protocol and does have a proper devicetree
implement, thus it could be a part of generic kernel.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>