nak: Move encode_sm* to to sm*.rs

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30141>

src/nouveau/compiler/nak/lib.rs

@@ -7,8 +7,6 @@ mod bitset;
 mod builder;
 mod calc_instr_deps;
 mod cfg;
-mod encode_sm50;
-mod encode_sm70;
 mod from_nir;
 mod ir;
 mod legalize;
@@ -26,6 +24,8 @@ mod opt_out;
 mod opt_uniform_instrs;
 mod qmd;
 mod repair_ssa;
+mod sm50;
+mod sm70;
 mod sph;
 mod spill_values;
 mod to_cssa;