quark_se: make EOI operations atomic

Some issues have been noted with nested interrupts on quark SE.
In particular, the wrong vector # being sent to the IOAPIC EOI
register. Now when doing EOI, we lock interrupts so that the act
of reading the current vector being serviced, and sending EOI
to both controllers happens atomically.

Change-Id: Id9ad992740e197bb9d4638764952b04a27c4af61
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>