nVMX: Refactor the EPT/VPID MSR cap check to make it readable

Use the EPT_CAP_* and VPID_CAP_* defines to declare which bits are
reserved in MSR_IA32_VMX_EPT_VPID_CAP.  Encoding the reserved bits in
a 64-bit literal is difficult to read, even more difficult to update,
and error prone, as evidenced by the check allowing bit 39 to be '1',
despite it being reserved to zero in Intel's SDM.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200207174244.6590-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>