parse sf prefix directly

[XYenChi]

want to discuss if adding a vendor attribute is better.

Although I think regarding vendor prefix as a intrinsic attribute may be a better way to maintain, but now parsing the string directly is easier.

[kito-cheng]

This PR will break doc gen like auto-generated/intrinsic_funcs.adoc

e.g.

-vint32m1_t __riscv_sf_vqmacc_4x8x4_i32m1(vint32m1_t vd, vint8m1_t vs1,
-                                         vint8mf2_t vs2, size_t vl);
+vint32m1_t __riscv_vqmaccu_4x8x4_i32m1(vint32m1_t vd, vint8m1_t vs1,
+                                       vint8m1_t vs2, size_t vl);