x86: mrst: Set vRTC's IRQ to level trigger type

When setting up the mpc_intsrc structure for vRTC's IRQ,
we need to set its irqflag to level trigger, otherwise
it will be taken as edge triggered and the vRTC IRQ will
fire only once, as there is never a EOI issued from the
IA core for it.

The original code worked in previous kernel. This is  because it
was configured to level trigger type by luck. It fell
into the default PCI trigger category which is level triggered.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
LKML-Reference: <20101111155019.12924.569.stgit@localhost.localdomain>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>