x86/RAS/AMD: Reduce the number of IPIs when prepping error injection

We currently use wrmsr_on_cpu() 4 times when prepping for an error
injection. This will generate 4 IPIs for each MSR write. We can reduce
the number of IPIs to 1 by grouping the MSR writes and executing them
serially on the appropriate CPU.

Suggested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Yazen Ghannam <Yazen.Ghannam@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aravind Gopalakrishnan <aravindksg.lkml@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1467968983-4874-3-git-send-email-bp@alien8.de


Signed-off-by: Ingo Molnar <mingo@kernel.org>