KVM: SVM: Add clean-bit for LBR state

This patch implements the clean-bit for all LBR related
state. This includes the debugctl, br_from, br_to,
last_excp_from, and last_excp_to msrs.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>