binding: update for xglCmdBindDescriptorSets()

This update makes it possible to bind multiple descriptor sets to the command
buffer.  We introduced intel_cmd_dset_data to hold the descriptor set offsets
in the global descriptor region as well as their dynamic offsets.  We also
changed the descriptor reading routines from

  intel_desc_set_read_surface()
  intel_desc_set_read_sampler()

to

  intel_desc_region_read_surface()
  intel_desc_region_read_sampler()

v2: fix a potential crash when allocation of dynamic_desc_indices fails
diff --git a/xgl.py b/xgl.py
index f9c6d44..0f89e5c 100644
--- a/xgl.py
+++ b/xgl.py
@@ -602,10 +602,13 @@
              Param("XGL_STATE_BIND_POINT", "stateBindPoint"),
              Param("XGL_DYNAMIC_STATE_OBJECT", "state")]),
 
-        Proto("void", "CmdBindDescriptorSet",
+        Proto("void", "CmdBindDescriptorSets",
             [Param("XGL_CMD_BUFFER", "cmdBuffer"),
              Param("XGL_PIPELINE_BIND_POINT", "pipelineBindPoint"),
-             Param("XGL_DESCRIPTOR_SET", "descriptorSet"),
+             Param("XGL_DESCRIPTOR_SET_LAYOUT_CHAIN", "layoutChain"),
+             Param("uint32_t", "layoutChainSlot"),
+             Param("uint32_t", "count"),
+             Param("const XGL_DESCRIPTOR_SET*", "pDescriptorSets"),
              Param("const uint32_t*", "pUserData")]),
 
         Proto("void", "CmdBindVertexBuffer",