raid6: riscv: Allow code to be compiled in userspace

To support userspace raid6test, this patch adds __KERNEL__ ifdef for kernel
header inclusions also userspace wrapper definitions to allow code to be
compiled in userspace.

This patch also drops the NSIZE macro, instead of using the vector length,
which can work for both kernel and user space.

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
Link: https://patch.msgid.link/20250718072711.3865118-5-zhangchunyan@iscas.ac.cn
Signed-off-by: Paul Walmsley <pjw@kernel.org>

lib/raid6/recov_rvv.c

@@ -4,13 +4,8 @@
  * Author: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
  */
 
-#include <asm/vector.h>
 #include <linux/raid/pq.h>
-
-static int rvv_has_vector(void)
-{
-	return has_vector();
-}
+#include "rvv.h"
 
 static void __raid6_2data_recov_rvv(int bytes, u8 *p, u8 *q, u8 *dp,
 				    u8 *dq, const u8 *pbmul,

lib/raid6/rvv.h

@@ -7,6 +7,23 @@
  * Definitions for RISC-V RAID-6 code
  */
 
+#ifdef __KERNEL__
+#include <asm/vector.h>
+#else
+#define kernel_vector_begin()
+#define kernel_vector_end()
+#include <sys/auxv.h>
+#include <asm/hwcap.h>
+#define has_vector() (getauxval(AT_HWCAP) & COMPAT_HWCAP_ISA_V)
+#endif
+
+#include <linux/raid/pq.h>
+
+static int rvv_has_vector(void)
+{
+	return has_vector();
+}
+
 #define RAID6_RVV_WRAPPER(_n)						\
 	static void raid6_rvv ## _n ## _gen_syndrome(int disks,		\
 					size_t bytes, void **ptrs)	\