nouveau: Fix swizzling for copies to rectangular textures

nouveau: Fix swizzling for copies to rectangular textures

nVidia hardware seems to swizzle rectangular texture (with width !=
height) coordinates by swizzling the lower bits and then adding the
higher bits from the larger dimension.
However, nv04_swizzle_bits ignores width and height and just
interleaves everything.
This causes problems with rectangular POT textures with height or
width 2048 or 4096 (but not 2048x1024 where it works by chance) since
the driver swizzles them in 1024x1024 chunks and gets the start
position for the non-first chunks wrong.
The following patch seems to fix those problems.