KVM: Portability: Move kvm_regs to <asm/kvm.h>

This patch moves structure kvm_regs to include/asm-x86/kvm.h.
Each architecture will need to create there own version of this
structure.

Signed-off-by: Jerone Young <jyoung5@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>