MIPS: ingenic: Drop obsolete code, merge the rest in setup.c

Drop a bootload of 10-years-old dirty code, that is not used anymore, as
it has been replaced with clean code over the ages.

Merge the very few bits left inside setup.c, so that everything is clean
and tidy now.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>