use es file explorer. it'll ask you to crop but you can resize the crop area to the whole pic so nothing is cropped.
I have been using Wallpaper Wizardrii which is one of my favorite android app for wallpapers.It allows me to set wallpaper without cropping.
*www.theandroidportal.com/wp-content/folder/2013/11/Android.jpg
Set your own images, Portrait, Landscape, and Crop; all with No Scroll or Scroll. Check out set Exact or Crop Exact! Set images from WW, file browser, or Android’s Gallery (Share as). Check Home App compatibility with No Scroll option (only). Invert, flip, rotate, greyscale, share, and resize images too. Using Wallpaper Wizarddi, you can use Image Full HD Wallpaper on your smartphone easily.
Source : Set Image As Full Wallpaper Without Cropping in Android