ggml-cpu: fix RVV checks in quants and repacking (#20682)

* ggml-cpu: refactor quants.c; add rvv check

* ggml-cpu: refactor; disable generic fallback

ggml/src/ggml-cpu/repack.cpp

@@ -1365,6 +1365,7 @@ void ggml_gemv_q8_0_4x8_q8_0_generic(int                        n,
     }
 }
 
+// Only enable these for RISC-V.
 #if defined __riscv_zvfh
 void ggml_gemv_q4_0_16x1_q8_0_generic(int n, float * GGML_RESTRICT s, size_t bs, const void * GGML_RESTRICT vx, const void * GGML_RESTRICT vy, int nr, int nc) {
     const int qk = QK8_0;
@@ -1568,6 +1569,7 @@ void ggml_gemv_q2_K_16x1_q8_K_generic(int n, float * GGML_RESTRICT s, size_t bs,
     assert(nc % 16 == 0);
 
     UNUSED(bs);
+    UNUSED(nr);
 
     const int nb = n / QK_K;
     const block_q2_Kx16 * x = (const block_q2_Kx16 *)vx;
@@ -2381,6 +2383,7 @@ void ggml_gemm_q8_0_4x8_q8_0_generic(int                        n,
     }
 }
 
+// Only enable these for RISC-V.
 #if defined __riscv_zvfh
 void ggml_gemm_q4_0_16x1_q8_0_generic(int n, float * GGML_RESTRICT s, size_t bs, const void * GGML_RESTRICT vx, const void * GGML_RESTRICT vy, int nr, int nc) {
     const int qk = QK8_0;