MIPS: jz4740: Rename jz4740 folders to ingenic

Now that all the jz4740 platform code has been removed, and we're left
with only a Kconfig and the cpu-feature-overrides.h file, finalize the
cleanup process by renaming the jz4740 and include/mach-jz4740 folders
to ingenic and include/mach-ingenic.

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