x86/vvmx: correctly emulate VMREAD

x86/vvmx: correctly emulate VMREAD

There is an issue with the original __vmread() in nested vmx mode:
emulation of a guest's VMREAD with invalid arguments leads to BUG().

Fix this by using vmread_safe() and reporting any kind of VMfail back
to the guest.

A new safe versions of get_vvmcs() macro and related functions are
introduced because of new function signatures and lots of existing
users.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>