KVM: VMX: introduce alloc_loaded_vmcs

commit f21f165ef922c2146cc5bdc620f542953c41714b upstream.

Group together the calls to alloc_vmcs and loaded_vmcs_init.  Soon we'll also
allocate an MSR bitmap there.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 4.4:
 - No loaded_vmcs::shadow_vmcs field to initialise
 - Adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>