selftest: kvm: Move struct kvm_x86_state to header

Those changes can avoid dereferencing pointer compile issue
when amx_test.c reference state->xsave.

Move struct kvm_x86_state definition to processor.h.

Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20211223145322.2914028-3-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>