crocus: uncomment the function crocus_clear_depth_stencil

What does this MR do and why?

Partial Depth/Stencil clearing remains broken with crocus as this function is commented out. Based on the commit history, it was in the disabled state since the introduction of the gallium driver for gfx4-7. It is understood that there must have been a reason to introduce this function in such a state.

This MR is to enable this function if possible, otherwise, to try to recognize and fix difficulties its enabling faces.