[POWERPC] iSeries: Fix section mismatch warning in lpevents

WARNING: vmlinux.o(.text+0x4f568): Section mismatch: reference to .init.text:.__alloc_bootmem (between '.setup_hvlpevent_queue' and '.process_hvlpevents')

setup_hvlpevent_queue is only called from __init code so make it __init
as well.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>