nvk: set optimization level to 3

nvk: set optimization level to 3

The refactor in a4f8fd9dd53d90307c98c1b4ed15ec1deaa8f8d3 changed NV50_PROG_OPTIMIZE
from 3 to 0.

Running with NV50_PROG_OPTIMIZE=0 causes some shaders to not compile. One example is
dEQP-VK.pipeline.monolithic.creation_cache_control.compute_pipelines.duplicate_single_recreate_explicit_caching
which fails with:
"Assertion `insn->src(src0 & FA_SRC_MASK).getFile() == FILE_GPR' failed"
A similar error also happen when testing Serious Sam Fusion 2017

Reviewed-by: M Henning <drawoc@darkrefraction.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25601>