KVM: VMX: Rename ops.h to vmx_ops.h

Rename ops.h to vmx_ops.h to allow adding a tdx_ops.h in the future
without causing massive confusion.

Trust Domain Extensions (TDX) is built on VMX, but KVM cannot directly
access the VMCS(es) for a TDX guest, thus TDX will need its own "ops"
implementation for wrapping the low level operations.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923183112.3030-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>