Add missing include which adds the prototype to plat_time_init().

Fixes: f932449c ("MIPS: ingenic: Drop obsolete code, merge the rest in setup.c")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>