ISA device drivers use the ISA source interrupt number in locations where

ISA device drivers use the ISA source interrupt number in locations where
the low level interrupt handler number should be used.  Change
setup_apic_irq_mapping() to allocate low level interrupt handler X (Xintr${X})
for any ISA interrupt X mentioned in the MP table.

Remove an assumption in the driver for the system clock (clock.c) that
interrupts mentioned in the MP table as delivered to IOAPIC #0 intpin Y
is handled by low level interrupt handler Y (Xintr${Y}) but don't assume
that low level interrupt handler 0 (Xintr0) is used.

Don't allocate two low level interrupt handlers for the system clock.
Reviewed by:	NOKUBI Hirotaka <hnokubi@yyy.or.jp>