x86, i8259: Only register sysdev if we have a real 8259 PIC

My platform makes use of the null_legacy_pic choice and oopses when doing
a shutdown as the shutdown code goes through all the registered sysdevs
and calls their shutdown method which in my case poke on a non-existing
i8259.  Imho the i8259 specific sysdev should only be registered if the
i8259 is actually there.

Do not register the sysdev function when the null_legacy_pic is used so
that the i8259 resume, suspend and shutdown functions are not called.

Signed-off-by: Adam Lackorzynski <adam@os.inf.tu-dresden.de>
LKML-Reference: <201007202218.o6KMIJ3m020955@imap1.linux-foundation.org>
Cc: Jacob Pan <jacob.jun.pan@intel.com>
Cc: <stable@kernel.org> 2.6.34
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>