irqchip: Appropriate __init annotation for const data

Init data marked const should be annotated with __initconst for
correctness and not __initdata.  And for those already __initconst,
they should be qualified as const at the compiler level too.
This also fixes LTO builds that otherwise fail with section mismatch
errors.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/alpine.LFD.2.20.1507241511551.1806@knanqh.ubzr


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>