r600g: skip repeating vs, gs, and tes shader binds

r600g: skip repeating vs, gs, and tes shader binds

The idea is taken from radeonsi. The code lacks some checks for null vs,
and I'm unsure about some changes against that, so I left it in place.

Some statistics for GTAⅣ:
Average tesselation bind skip per frame: ≈350
Average geometric shaders bind skip per frame: ≈260
Skip of binding vertex ones occurs rarely enough to not get into per-frame
counter at all, so I just gonna say: it happens.

v2: I've occasionally removed an empty line, don't do this.
v3: return a check for null tes and gs back, while I haven't figured out
the way to move stride assignment to r600_update_derived_state() (as it
is in radeonsi).

Signed-off-by: Constantine Kharlamov <Hi-Angel@yandex.ru>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>