anv+hasvk: Use driconf to disable 16-bit for zink.

anv+hasvk: Use driconf to disable 16-bit for zink.

The HW can technically execute 16-bit operations, but the restrictions on
16-bit ALU ops are so great that it ends up not being a win for
GLES-on-Vulkan to lower mediump to 16-bit operations, at least with the
current state of the Intel compiler.  This brings zink-on-anv in line with
iris and angle-on-anv for mediump behavior (ANGLE uses RelaxedPrecision,
which we ignore).

Perf on some angle traces on my brya (ADL) and i9-9900K (CFL):

ADL zink pubg_mobile_battle_royale:  +13.4574% +/- 5.2046% (n=5)
CFL zink pubg_mobile_battle_royale:  +29.5332% +/- 0.646585% (n=6)
ADL zink aztec_ruins_high:           +5.78027% +/- 4.80645% (n=4)
CFL zink aztec_ruins_high:           -1.10641% +/- 0.140562% (n=12)
ADL zink trex_200:                   +5.86956% +/- 2.09633% (n=10)
CFL zink trex_200:                   +9.72136% +/- 0.749261% (n=10)

Reviewed-by: Ivan Briano <ivan.briano@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21775>