x86/msr: Fix fallout from mostly c/s 832c180

x86/msr: Fix fallout from mostly c/s 832c180

 * Fix the shim build by providing a !CONFIG_HVM declaration for
   hvm_get_guest_bndcfgs(), and removing the introduced
   ASSERT(is_hvm_domain(d))'s.  They are needed for DCE to keep the build
   working.  Furthermore, in this way, the risk of runtime type confusion is
   removed.
 * Revert the de-const'ing of the vcpu pointer in vmx_get_guest_bndcfgs().
   vmx_vmcs_enter() really does mutate the vcpu, and may cause it to undergo a
   full de/reschedule, which is contrary to the programmers expectation of
   hvm_get_guest_bndcfgs().  guest_rdmsr() was always going to need to lose
   its const parameter, and this was the correct time for it to happen.
 * The MSRs in vcpu_msrs are in numeric order.  Re-position XSS to match.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>