nvc0/ir: make sure to align the second arg of TXD to 4, as we do for TEX

nvc0/ir: make sure to align the second arg of TXD to 4, as we do for TEX

This was handled in handleTEX(), however the way the logic works, those
extra arguments aren't added on by then, so it did nothing. Instead we
must duplicate that bit here. GK110 appears to complain about
MISALIGNED_GPR, however it's reasonable to believe that GK104 has the
same requirements.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95403
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>