KVM: SVM: Move guest register save out of interrupts disabled section

Saving guest registers is just a memory copy, and does not need to be in the
critical section.  Move outside the critical section to improve latency a
bit.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>