nVMX: Fix name of macro defining EPT execute only capability

Rename EPT_CAP_WT to EPT_CAP_EXEC_ONLY.  In x86, "WT" generally refers to
write-through memtype, and is especially confusing considering that EPT
capabilities also report UC and WB memtypes.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211125012857.508243-35-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>