From your controller you just set the value(s) that you want to display, and have the HTML template render your value(s).
Change your markup to:
<button ng-model="visibilityStatus" ng-click="visibilityEnable()" ng-bind="buttonText"></button>
alternate markup:
<button ng-model="visibilityStatus" ng-click="visibilityEnable()">{{buttonText}}</button>
And in your controller:
$scope.buttonText = 'Enable'
$scope.visibilityEnable = function(){
$scope.buttonText = $scope.buttonText === 'Enable' ? 'Disable' : 'Enable';
}