intel: rework cmd helpers

In the hope that the new helpers are easier to use.

An important change is that the units used for a writer are changed from
dwords to bytes.  Helpers may still use dwords when it is more natural.
diff --git a/icd/intel/cmd.h b/icd/intel/cmd.h
index 4d9daf7..5443de7 100644
--- a/icd/intel/cmd.h
+++ b/icd/intel/cmd.h
@@ -128,7 +128,7 @@
 
 struct intel_cmd_shader {
     const struct intel_pipeline_shader *shader;
-    XGL_UINT kernel_pos;
+    uint32_t kernel_offset;
 };
 
 /*
@@ -199,12 +199,11 @@
 };
 
 struct intel_cmd_writer {
+    XGL_SIZE size;
     struct intel_bo *bo;
     void *ptr;
 
-    /* in DWords */
-    XGL_UINT size;
-    XGL_UINT used;
+    XGL_SIZE used;
 };
 
 struct intel_cmd {
@@ -252,7 +251,7 @@
         &cmd->writers[INTEL_CMD_WRITER_BATCH];
 
     if (used)
-        *used = sizeof(uint32_t) * writer->used;
+        *used = writer->used;
 
     return writer->bo;
 }