xilinx_spi: Switch to iomem functions and support little endian.

This patch changes the out_(be)(8|16|32) and in_(be)(8|16|32) calls to 32 bits ioread/iowrite.

The read and write function are attached to the internal struct as callbacks, callback
is selected depending on endianess.

This will also build on platforms not supporting the in/out calls for instance x86.

Acked-by: Grant Likely <grant.likely@secretlab.ca>
Tested-by: John Linn <John.Linn@xilinx.com>
Signed-off-by: Richard Röjfors <richard.rojfors@mocean-labs.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/spi/xilinx_spi.h

@@ -4,11 +4,13 @@
 /**
  * struct xspi_platform_data - Platform data of the Xilinx SPI driver
  * @num_chipselect:	Number of chip select by the IP
+ * @little_endian	If registers should be accessed little endian or not
  * @devices:		Devices to add when the driver is probed.
  * @num_devices:	Number of devices in the devices array.
  */
 struct xspi_platform_data {
 	u16 num_chipselect;
+	bool little_endian;
 	struct spi_board_info *devices;
 	u8 num_devices;
 };