bsp/atsam: Fix cache / DMA handling in SPI.

This patch fixes the cache handling for the atsam SPI driver. Note that
this solution might doesn't have the best performance for small packets.

bsps/arm/atsam/headers.am

@@ -11,6 +11,7 @@ include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/atsam-clock-
 include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/atsam-i2c.h
 include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/atsam-spi.h
 include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/i2c.h
+include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/iocopy.h
 include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/irq.h
 include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/pin-config.h
 include_bsp_HEADERS += ../../../../../../bsps/arm/atsam/include/bsp/power.h

bsps/arm/atsam/include/bsp/iocopy.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2018 embedded brains GmbH.  All rights reserved.
+ *
+ *  embedded brains GmbH
+ *  Dornierstr. 4
+ *  82178 Puchheim
+ *  Germany
+ *  <rtems@embedded-brains.de>
+ *
+ * The license and distribution terms for this file may be
+ * found in the file LICENSE in this distribution or at
+ * http://www.rtems.org/license/LICENSE.
+ */
+
+#ifndef ATSAM_IOCOPY_H
+#define ATSAM_IOCOPY_H
+
+#include <rtems.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/*
+ * Note: This functions are for copying from or to memory that is marked as
+ * Peripheral memory. In this regions a misaligned access is not allowed.
+ * Therefore memcopy would not work in all cases.
+ */
+void atsam_copy_to_io(void *dst, const void *src, size_t n);
+void atsam_copy_from_io(void *dst, const void *src, size_t n);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* ATSAM_IOCOPY_H */