of/mips: Cleanup some include directives/files.

The __init directives should go on the definitions of things, not the
declaration, also __init is meaningless for inline functions, so
remove it from prom.h.  This allows us to get rid of a useless
#include, but most of the rest of them are useless too, so kill them
as well.

If of_i2c.c needs irq definitions, it should include linux/irq.h
directly, not assume indirect inclusion via asm/prom.h.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>