x86: fix CMCI injection

x86: fix CMCI injection

This fixes the wrong use of literal vector 0xF7 with an "int"
instruction (invalidated by 25113:14609be41f36) and the fact that doing
the injection via a software interrupt was never valid anyway (because
cmci_interrupt() acks the LAPIC, which does the wrong thing if the
interrupt didn't get delivered though it).

In order to do latter, the patch introduces send_IPI_self(), at once
removing two opend coded uses of "genapic" in the IRQ handling code.

Reported-by: Yongjie Ren <yongjie.ren@intel.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Yongjie Ren <yongjie.ren@intel.com>
Acked-by: Keir Fraser <keir@xen.org>