discovered with IOAPIC disabled.

The problem was that drivers/serial/8250_acpi.c found COM1 in the ACPI
namespace and called acpi_register_gsi() to set up its IRQ.  ACPI tells us
that the COM1 IRQ is edge triggered, active high, but acpi_register_gsi()
was ignoring the edge_level argument, so it blindly set the COM1 IRQ to be
level-triggered.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org