panfrost: Rewrite u-interleaving code

panfrost: Rewrite u-interleaving code

Rather than using a magic lookup table with no explanations, let's add
liberal comments to the code to explain what this tiling scheme is and
how to encode/decode it efficiently.

It's not so mysterious after all -- just reordering bits with some XORs
thrown in.

v2: Correct copyright identifier. Fix spelling error. Switch space_4 to
a LUT. Fix comment typo. Use LUT instead of space_x tricks. Fallback on
generic rather than split up unaligned writes.

v3: Correct stride order (fixes crash loading). Correct coordinate
system mishap.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Tested-by: Andreas Baierl <ichgeh@imkreisrum.de>