x86/vvmx: Fix handing of the MSR_BITMAP field with VMCS shadowing

x86/vvmx: Fix handing of the MSR_BITMAP field with VMCS shadowing

Currently, the following sequence of actions:

 * VMPTRLD (creates a mapping, likely pointing at gfn 0 for an empty vmcs)
 * VMWRITE CPU_BASED_VM_EXEC_CONTROL (completed by hardware)
 * VMWRITE MSR_BITMAP (completed by hardware)
 * VMLAUNCH

results in an L2 guest running with ACTIVATE_MSR_BITMAP set, but Xen using a
stale mapping (likely gfn 0) when reading the interception bitmap.  The
MSR_BITMAP field needs unconditionally intercepting even with VMCS shadowing,
so Xen's mapping of the bitmap can be updated.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>