[POWERPC] Fix spurious vectors on weird MPIC

The weird TSI 10x MPIC needs an EOI after getting a spurious vector.  This
patch uses the existing MPIC_SPV_EOI flag to fix this issue.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>