KVM: VMX: Add vmx_setup_uret_msr() to handle lookup and swap

Add vmx_setup_uret_msr() to wrap the lookup and manipulation of the uret
MSRs array during setup_msrs().  In addition to consolidating code, this
eliminates move_msr_up(), which while being a very literally description
of the function, isn't exacly helpful in understanding the net effect of
the code.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923180409.32255-12-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>