st/mesa: fix bitmap,drawpix,drawtex for PIPE_CAP_TGSI_TEXCOORD

NOTE: Changed the semantic index for the drawtex coordinate to
be the texture unit index instead of always 0.
Not sure if this is correct but since the value seems to depend
on the unit it would make sense to use different varying slots.

src/mesa/state_tracker/st_cb_drawpixels.c

@@ -294,6 +294,9 @@ static void *
 make_passthrough_vertex_shader(struct st_context *st, 
                                GLboolean passColor)
 {
+   const unsigned texcoord_semantic = st->needs_texcoord_semantic ?
+      TGSI_SEMANTIC_TEXCOORD : TGSI_SEMANTIC_GENERIC;
+
    if (!st->drawpix.vert_shaders[passColor]) {
       struct ureg_program *ureg = ureg_create( TGSI_PROCESSOR_VERTEX );
 
@@ -307,7 +310,7 @@ make_passthrough_vertex_shader(struct st_context *st,
       
       /* MOV result.texcoord0, vertex.attr[1]; */
       ureg_MOV(ureg, 
-               ureg_DECL_output( ureg, TGSI_SEMANTIC_GENERIC, 0 ),
+               ureg_DECL_output( ureg, texcoord_semantic, 0 ),
                ureg_DECL_vs_input( ureg, 1 ));
       
       if (passColor) {