KVM: prepare for KVM_(S|G)ET_MP_STATE on other architectures

Highlight the aspects of the ioctls that are actually specific to x86
and ia64. As defined restrictions (irqchip) and mp states may not apply
to other architectures, these parts are flagged to belong to x86 and ia64.

In preparation for the use of KVM_(S|G)ET_MP_STATE by s390.
Fix a spelling error (KVM_SET_MP_STATE vs. KVM_SET_MPSTATE) on the way.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>