Fix invalid channel order in tcuTextureUtil.

Fix invalid channel order in tcuTextureUtil.

- tcuTextureUtil stored channel bit depths of combined formats in
  swizzled form. Reorder combined formats so that depth of the first
  channel is in the first component and depth of the second channel is
  in the second, not 4th, component. Since these values are swizzled
  using the channel read swizzle when queried, this change prevents
  combined formats from being swizzled two times.

Bug: 19846703
Change-Id: I2afd47ae2ecb9f93f982ef2c9dbd24f5223bf172