x86: fix unmaskable msi assignment issue.

x86: fix unmaskable msi assignment issue.

Currently, unmasked msi irq's EOI write is deferred untile guest
writes EOI, so needs to keep eoi_vector unchanged before guest writes
EOI. However, irq migration breaks the assumption and changs
eoi_vector when interrupts are generated through new vector.

The patch removes the dependency for eoi_vector and directly recoreds
the irq info in the EOI stack, and when guest writes EOI, just do the
physical EOI for the specific irq(recorded in EOI stack)on the cpus
according to the cpu_eoi_map.

Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>