BGRA8 texture support also applies to texture copy operations.

Change-Id: Ie3920585904c67ddf1b5b308eff60bc83f9e195b
Reviewed-on: https://swiftshader-review.googlesource.com/5142Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>