powerpc: rtc_cmos_setup: assign interrupts only if there is i8259 PIC

i8259 PIC is disabled on MPC8610HPCD boards, thus currently rtc-cmos
driver fails to probe.

To fix the issue, we lookup the device tree for "chrp,iic" and
"pnpPNP,000" compatible devices, and if not found we do not assign RTC
IRQ and assuming that i8259 was disabled.

Though this patch fixes RTC on some boards (and surely should not break
any other), the whole approach is still broken. We can't easily fix this
though, because old device trees do not specify i8259 interrupts for the
cmos rtc node.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>