[XEN][POWERPC] Generalized parallel IPI handlers

[XEN][POWERPC] Generalized parallel IPI handlers
Our problem with x86 do_IRQ is that it does not respect IRQ_PER_CPU, so
make our logic reflect that generically.  We remove the spin lock in
this case, since the programming convention is to update irq descs
atomically (if at all).  This patch allows read_clocks to work properly.
Signed-off-by: Amos Waterland <apw@us.ibm.com>
Signed-off-by: Jimi Xenidis <jimix@watson.ibm.com>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
--HG--
extra : transplant_source : %1E%1Ac%40%81%29%BE%A2%D8%7FH%5CR%F1%BE%21%AD%A3_%F0