svga: add a few minor comments

Trivial.

src/gallium/drivers/svga/svga_resource_buffer_upload.c

@@ -138,7 +138,10 @@ svga_buffer_create_hw_storage(struct svga_screen *ss,
 }
 
 
-
+/**
+ * Allocate graphics memory for vertex/index/constant/etc buffer (not
+ * textures).
+ */
 enum pipe_error
 svga_buffer_create_host_surface(struct svga_screen *ss,
                                 struct svga_buffer *sbuf)

src/gallium/drivers/svga/svga_screen_cache.c

@@ -461,6 +461,7 @@ svga_screen_surface_create(struct svga_screen *svgascreen,
             key->cachable);
 
    if (cachable) {
+      /* Try to re-cycle a previously freed, cached surface */
       if (key->format == SVGA3D_BUFFER) {
          SVGA3dSurfaceFlags hint_flag;
 
@@ -521,6 +522,7 @@ svga_screen_surface_create(struct svga_screen *svgascreen,
    }
 
    if (!handle) {
+      /* Unable to recycle surface, allocate a new one */
       unsigned usage = 0;
 
       if (!key->cachable)