dri: add __DRI_IMAGE_FORMAT_SXRGB8

Add format definition and required plumbing to create images.

Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3077>

include/GL/internal/dri_interface.h

 #define __DRI_IMAGE_FORMAT_UYVY         0x1013
 #define __DRI_IMAGE_FORMAT_XBGR16161616F 0x1014
 #define __DRI_IMAGE_FORMAT_ABGR16161616F 0x1015
+#define __DRI_IMAGE_FORMAT_SXRGB8       0x1016
 
 #define __DRI_IMAGE_USE_SHARE		0x0001
 #define __DRI_IMAGE_USE_SCANOUT		0x0002
 
 #define __DRI_IMAGE_FOURCC_SARGB8888	0x83324258
 #define __DRI_IMAGE_FOURCC_SABGR8888	0x84324258
+#define __DRI_IMAGE_FOURCC_SXRGB8888	0x85324258
 
 /**
  * Queryable on images created by createImageFromNames.

src/loader/loader_dri3_helper.c

    case  __DRI_IMAGE_FORMAT_ABGR2101010:
    case  __DRI_IMAGE_FORMAT_SARGB8:
    case  __DRI_IMAGE_FORMAT_SABGR8:
+   case  __DRI_IMAGE_FORMAT_SXRGB8:
       return 4;
    case __DRI_IMAGE_FORMAT_XBGR16161616F:
    case __DRI_IMAGE_FORMAT_ABGR16161616F:
    switch (format) {
    case __DRI_IMAGE_FORMAT_SARGB8: return __DRI_IMAGE_FOURCC_SARGB8888;
    case __DRI_IMAGE_FORMAT_SABGR8: return __DRI_IMAGE_FOURCC_SABGR8888;
+   case __DRI_IMAGE_FORMAT_SXRGB8: return __DRI_IMAGE_FOURCC_SXRGB8888;
    case __DRI_IMAGE_FORMAT_RGB565: return DRM_FORMAT_RGB565;
    case __DRI_IMAGE_FORMAT_XRGB8888: return DRM_FORMAT_XRGB8888;
    case __DRI_IMAGE_FORMAT_ARGB8888: return DRM_FORMAT_ARGB8888;

src/mesa/drivers/dri/common/dri_util.c

       .image_format = __DRI_IMAGE_FORMAT_SARGB8,
       .mesa_format  =        MESA_FORMAT_B8G8R8A8_SRGB,
    },
+   {
+      .image_format = __DRI_IMAGE_FORMAT_SXRGB8,
+      .mesa_format  =        MESA_FORMAT_B8G8R8X8_SRGB,
+   },
    {
       .image_format = __DRI_IMAGE_FORMAT_R16,
       .mesa_format  =        MESA_FORMAT_R_UNORM16,