How to create this pattern in Photoshop or Illustrator

Plastic Grainy is a Substance 3D material that is available through the Substance 3D Community Assets that's pretty close:

https://substance3d.adobe.com/community-assets/assets/a08477ed227779c3bc5b362d024185cc1fc59a6b

Or here's another approach to make a pattern like the picture that you could try in Photoshop:

1. In a new document, set the foreground and background colors to the default black and white (click on the small color tiles at the bottom of the Toolbar)
2. Go to Filter > Render > Clouds
3. Go to Filter > Render > Difference Clouds
4. Duplicate the Background layer
5. Add a Levels Adjustment layer (go to the bottom of the Layers panel, click on the middle icon, and select Levels...)
6. In the Properties panel, move the sliders under the histogram to make what you'll use as a mask:
   • the left slider a bit to the right to make thicker black borders
   • the middle slider to the left
   • the right slider to the left to make solid white sections
7. Select the adjustment layer and the duplicated difference clouds layer, right-click, and select Merge Layers from the contextual menu
8. Select the Background layer and click the Layer Mask icon to add a layer mask
9. Copy the merged layer, select the new layer mask, Alt+click (Windows) or Option+click (macOS) to show just the layer mask, and paste
10. Toggle off the visibility of the merged layer
11. Double-click what was the Background layer and is now Layer 0 to add some Layer Styles
    • Color Overlay - give it a gray color
    • Bevel & Emboss, Contour - in the options under Elements, set the Contour to the 2nd from the right on the top row and select Anti-aliased (you can also add your own Contour. Double-click the new contour to modify it. 
12. Make a new layer, move it below Layer 0, sample the darker shadowy gray, and use that color to fill this layer

If you want the edges around the sections to be smoother, then Ctrl+click (Command+click) on the layer mask to load the selection, invert the selection (Ctrl+Shift+I, Command+Shift +I), go to Select > Modify > Smooth, increase the radius, and fill with black.

In Photoshop, you could start with a 50% grey layer then use filters to Add Noise , add Gaussian Blur, then use use Find Edges before adjusting it with a curve. However the best tool for creating such procedural patterns for height/bump maps is Substance 3D Designer. It will output the bump map directly (along with the BaseColor, Roughness and Normal maps if you require them).

Dave

@Paulo1988 it's been awhile for me to creating a pattern from an image in Illustrator, but I did create a video a few years back for that, called How to Create a Pattern Swatch from an Image in Illustrator