nvc0: implement support for maxwell texture headers

nvc0: implement support for maxwell texture headers

Adds support for the new TIC layout that's present on Maxwell GPUs,
heavily based on the code for the existing layout.

This code is required for GM20x support.  While GM10x supports the older
layout still, this commit switches it to use the updated version instead.

Piglit testing shows zero regressions on GM107.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Acked-by: Ilia Mirkin <imirkin@alum.mit.edu>