freedreno/ir3: Lower texture instructions used only for f2f16 to 16-bit.

freedreno/ir3: Lower texture instructions used only for f2f16 to 16-bit.

2.5% improvement in gfxbench vk-5-normal.  No obvious change on
gl-5-normal.

shader-db on Rob's android shaders:

total instructions in shared programs: 770644 -> 770595 (<.01%)
instructions in affected programs: 14880 -> 14831 (-0.33%)
total nops in shared programs: 167784 -> 167860 (0.05%)
nops in affected programs: 3351 -> 3427 (2.27%)
total non-nops in shared programs: 602860 -> 602735 (-0.02%)
non-nops in affected programs: 10523 -> 10398 (-1.19%)
total mov in shared programs: 19313 -> 19286 (-0.14%)
mov in affected programs: 365 -> 338 (-7.40%)
total cov in shared programs: 18075 -> 17978 (-0.54%)
cov in affected programs: 566 -> 469 (-17.14%)
total dwords in shared programs: 1612848 -> 1612596 (-0.02%)
dwords in affected programs: 13882 -> 13630 (-1.82%)
total last-baryf in shared programs: 56144 -> 55975 (-0.30%)
last-baryf in affected programs: 482 -> 313 (-35.06%)
total full in shared programs: 36094 -> 36092 (<.01%)
full in affected programs: 10 -> 8 (-20.00%)
total sstall in shared programs: 66986 -> 66923 (-0.09%)
sstall in affected programs: 1392 -> 1329 (-4.53%)
total systall in shared programs: 91244 -> 91072 (-0.19%)
systall in affected programs: 1194 -> 1022 (-14.41%)
total (sy) in shared programs: 4316 -> 4321 (0.12%)
(sy) in affected programs: 19 -> 24 (26.32%)

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16465>