nir/lower_idiv: add new llvm-based path

nir/lower_idiv: add new llvm-based path

v2: make variable names snake_case
v2: minor cleanups in emit_udiv()
v2: fix Panfrost build failure
v3: use an enum instead of a boolean flag in nir_lower_idiv()'s signature
v4: remove nir_op_urcp
v5: drop nv50 path
v5: rebase
v6: add back nv50 path
v6: add comment for nir_lower_idiv_path enum
v7: rename _nv50/_llvm to _fast/_precise
v8: fix etnaviv build failure

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>