pixelflinger: Fix function naming typo: gglBitBlti

From the functionality, the function gglBitBlti() implemented bit-block
(image) transfer operation in which several bitmaps are combined into
one using a raster operator.  Renaming to gglBitBlit() should be
explicit.

Change-Id: I23886623b5421131cf7c7bfb8ec67c3809566c93