[SVM] Return the shadow EFER value on guest EFER reads.

[SVM] Return the shadow EFER value on guest EFER reads.

Return the shadow of the guest's EFER instead of the VMCB.  This helps
with things such as the unlikely event the guest wants to check EFER.LME
immediately after setting it (The VMCB's EFER.LME remains clear until
the guest enables paging).

Signed-off-by: Travis Betak <travis.betak@amd.com>