Revert "intel: Make RGB renderbuffers use XRGB8888 like we do for RGB system buffers."

This reverts commit 4598942b1b.

XRGB8888 doesn't work as intended.  Revert this for now, and we'll revisit it
for 7.8 or something.

src/mesa/drivers/dri/intel/intel_fbo.c

@@ -126,7 +126,7 @@ intel_alloc_renderbuffer_storage(GLcontext * ctx, struct gl_renderbuffer *rb,
    case GL_RGB16:
       rb->Format = MESA_FORMAT_ARGB8888;
       rb->DataType = GL_UNSIGNED_BYTE;
-      irb->texformat = MESA_FORMAT_XRGB8888;
+      irb->texformat = MESA_FORMAT_ARGB8888; /* XXX: Need xrgb8888 */
       cpp = 4;
       break;
    case GL_RGBA:
@@ -314,6 +314,10 @@ intel_create_renderbuffer(gl_format format)
       irb->Base.DataType = GL_UNSIGNED_BYTE;
       break;
    case MESA_FORMAT_XRGB8888:
+      /* XXX this is a hack since XRGB surfaces don't seem to work
+       * properly yet.  Reading the alpha channel returns 0 instead of 1.
+       */
+      format = MESA_FORMAT_ARGB8888;
       irb->Base._BaseFormat = GL_RGB;
       irb->Base.DataType = GL_UNSIGNED_BYTE;
       break;