gallium: Add a cap bit for OpenCL-style extended integer functions

Iris will eventually enable this.  Looking at the header files, it looks
like Midgard could also enable it.  Basically, any GPU that fully
supports OpenCL can.

v2: Add default value to u_screen.c.  Suggested by Caio.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/767>

src/gallium/auxiliary/util/u_screen.c

@@ -404,6 +404,9 @@ u_pipe_screen_get_param_defaults(struct pipe_screen *pscreen,
    case PIPE_CAP_MAX_VERTEX_BUFFERS:
       return 16;
 
+   case PIPE_CAP_OPENCL_INTEGER_FUNCTIONS:
+      return 0;
+
    default:
       unreachable("bad PIPE_CAP_*");
    }

src/gallium/docs/source/screen.rst

@@ -565,6 +565,7 @@ The integer capabilities:
 * ``PIPE_CAP_TWO_SIDED_COLOR``: Driver supports two-sided coloring.
 * ``PIPE_CAP_CLIP_PLANES``: Driver supports user-defined clip-planes.
 * ``PIPE_CAP_MAX_VERTEX_BUFFERS``: Number of supported vertex buffers.
+* ``PIPE_CAP_OPENCL_INTEGER_FUNCTIONS``: Driver supports extended OpenCL-style integer functions.  This includes averge, saturating additiong, saturating subtraction, absolute difference, count leading zeros, and count trailing zeros.
 
 .. _pipe_capf:
 

src/gallium/include/pipe/p_defines.h

@@ -910,6 +910,7 @@ enum pipe_cap
    PIPE_CAP_TWO_SIDED_COLOR,
    PIPE_CAP_CLIP_PLANES,
    PIPE_CAP_MAX_VERTEX_BUFFERS,
+   PIPE_CAP_OPENCL_INTEGER_FUNCTIONS,
 };
 
 /**