etnaviv: GC7000: Texture descriptors

etnaviv: GC7000: Texture descriptors

Create a separate implementation file with texture-descriptor-based
sampler views and sampler states. Initialize the one or the other
based on the GPU. There is so little in common that this seemed more
appropriate that keeping them as one type of state object would
only be confusing.

This commit is actually a combiation of the original commit by
Wladimir, fixes and TS implementation from Jonathan and changed to
use softpin by Lucas.

Signed-off-by: Wladimir J. van der Laan <laanwj@gmail.com>
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Jonathan Marek <jonathan@marek.ca>