sh: intc: alloc_bootmem() -> kzalloc() conversion.

Now that the slab allocators are available much earlier, this triggers a
the slab_is_available() warning when registering the interrupt
controller. Convert to kzalloc() with GFP_NOWAIT, as per the generic
changes.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>