arc: remove '__init' for setup_processor() and arc_init_IRQ()

They haven't '__init' in definition, but has '__init' in declaration.
And normal function start_kernel_secondary() may call setup_processor()
which will call arc_init_IRQ().

So need remove '__init' for both of them. The related warning (with
allmodconfig):

    MODPOST vmlinux.o
  WARNING: vmlinux.o(.text+0x3084): Section mismatch in reference from the function start_kernel_secondary() to the function .init.text:setup_processor()
  The function start_kernel_secondary() references
  the function __init setup_processor().
  This is often because start_kernel_secondary lacks a __init
  annotation or the annotation of setup_processor is wrong.

Signed-off-by: Chen Gang <gang.chen@asianux.com>