KVM: SVM: Rename vmcb->virt_ext to vmcb->misc_ctl2

KVM: SVM: Rename vmcb->virt_ext to vmcb->misc_ctl2

'virt' is confusing in the VMCB because it is relative and ambiguous.
The 'virt_ext' field includes bits for LBR virtualization and
VMSAVE/VMLOAD virtualization, so it's just another miscellaneous control
field. Name it as such.

While at it, move the definitions of the bits below those for
'misc_ctl' and rename them for consistency.

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260303003421.2185681-20-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>