MIPS: ingenic: remove unused platform_data header file

There are no users of this headers file in the kernel.
All users are likely migrated to device tree which is a good thing.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Cercueil <paul@crapouillou.net>
Cc: Harvey Hunt <harveyhuntnexus@gmail.com>
Cc: linux-mips@vger.kernel.org
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>