MAINTAINERS: add KVM x86 reviewers

MAINTAINERS: add KVM x86 reviewers

This is probably overdue---KVM x86 has quite a few contributors that
usually review each other's patches, which is really helpful to me.
Formalize this by listing them as reviewers.  I am including people
with various expertise:

- Joerg for SVM (with designated reviewers, it makes more sense to have
him in the main KVM/x86 stanza)

- Sean for MMU and VMX

- Jim for VMX

- Vitaly for Hyper-V and possibly SVM

- Wanpeng for LAPIC and paravirtualization.

Please ack if you are okay with this arrangement, otherwise speak up.

In other news, Radim is going to leave Red Hat soon.  However, he has
not been very much involved in upstream KVM development for some time,
and in the immediate future he is still going to help maintain kvm/queue
while I am on vacation.  Since not much is going to change, I will let
him decide whether he wants to keep the maintainer role after he leaves.

Acked-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: Wanpeng Li <wanpengli@tencent.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>