KVM: SVM: fix cr8 intercept window

KVM: SVM: fix cr8 intercept window

We always disable cr8 intercept in its handler, but only re-enable it
if handling KVM_REQ_EVENT, so there can be a window where we do not
intercept cr8 writes, which allows an interrupt to disrupt a higher
priority task.

Fix this by disabling intercepts in the same function that re-enables
them when needed. This fixes BSOD in Windows 2008.

Cc: <[email protected]>
Signed-off-by: Radim Krčmář <[email protected]>
Reviewed-by: Marcelo Tosatti <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>