Implement storedevs, prepare to port littlefs

kernel/std/include/string.h

@@ -0,0 +1,16 @@
+#ifndef STD_STRING_H_
+#define STD_STRING_H_
+
+#include <stddef.h>
+
+void *memset(void *p, int c, size_t n);
+void *memcpy(void *dst, const void *src, size_t n);
+size_t strlen(char *s);
+int strcmp(const char *a, const char *b);
+size_t strcspn(const char *s, const char *reject);
+size_t strspn(const char *s, const char *accept);
+char *strcpy(char *dest, const char *src);
+char *strchr(const char *s, int c);
+int memcmp(const void *s1, const void *s2, int len);
+
+#endif // STD_STRING_H_