vmm(4)/vmx: avoid VPID leakage by allocating at vcpu init.

vmm(4)/vmx: avoid VPID leakage by allocating at vcpu init.

VPID allocation being dependent on the host and guest config
(consequently pushing it into the reset register handler) creates
a leak where previous VPIDs are not freed if the hypervisor program
resets a vcpu's registers.

Recent SVM related changes pulled the VPID (ASID in AMD world)
allocation up into vcpu initialization. This change does the same
for VMX and cleans up appropriate logic. Minor changes to keep SVM
and VMX styles in line with each other.

ok bluhm@