Fixed negative X coord, tile index for 8bpp images and vertical
and horizontal flip.

X Coordinate is in two's complement 9-bit format.
Fixed bug when horizontal and vertical flags is set at the same time.
For 8bpp images, we don't need to multiply the tile number by two.
  This  is neede for 4bpp since the NDS works with tiles of 2 px / 1 byte
  and the internal data array in images with 1 px / 1 entry.