Replace sprintf()->snprintf() and strcpy()->strlcpy()

The strcpy() and sprintf() functions are deprecated on some platforms.
Care is needed to ensure correct size is used.  If some platforms
miss snprintf, we can add a #define to sprintf, likewise strlcpy().

The biggest change is adding a size parameter to zfs_id_to_fuidstr().

The various *_impl_get() functions are only used on linux and have
not yet been updated.

module/icp/algs/modes/gcm.c

@@ -857,7 +857,7 @@ gcm_impl_init(void)
 		    sizeof (gcm_fastest_impl));
 	}
 
-	strcpy(gcm_fastest_impl.name, "fastest");
+	strlcpy(gcm_fastest_impl.name, "fastest", GCM_IMPL_NAME_MAX);
 
 #ifdef CAN_USE_GCM_ASM
 	/*
@@ -969,7 +969,7 @@ gcm_impl_set(const char *val)
 	return (err);
 }
 
-#if defined(_KERNEL)
+#if defined(_KERNEL) && defined(__linux__)
 #include <linux/mod_compat.h>
 
 static int