KVM: Use standard CR8 flags, and fix TPR definition

Intel manual (and KVM definition) say the TPR is 4 bits wide.  Also fix
CR8_RESEVED_BITS typo.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>