vc4: Enable V3D 2.6.

This version of the chip is present on the Cygnus-based 911360 enterprise
phone platform.  It appears to be completely backwards compatible.

Author: anholt

src/gallium/drivers/vc4/vc4_screen.c

@@ -587,7 +587,7 @@ vc4_get_chip_info(struct vc4_screen *screen)
         uint32_t minor = (ident1.value >> 0) & 0xf;
         screen->v3d_ver = major * 10 + minor;
 
-        if (screen->v3d_ver != 21) {
+        if (screen->v3d_ver != 21 && screen->v3d_ver != 26) {
                 fprintf(stderr,
                         "V3D %d.%d not supported by this version of Mesa.\n",
                         screen->v3d_ver / 10,