spi: SuperH MSIOF SPI Master driver V2

This patch is V2 of SPI Master support for the SuperH MSIOF.
Full duplex, spi mode 0-3, active high cs, 3-wire and lsb
first should all be supported, but the driver has so far
only been tested with "mmc_spi".

The MSIOF hardware comes with 32-bit FIFOs for receive and
transmit, and this driver simply breaks the SPI messages
into FIFO-sized chunks. The MSIOF hardware manages the pins
for clock, receive and transmit (sck/miso/mosi), but the chip
select pin is managed by software and must be configured as
a regular GPIO pin by the board code.

Performance wise there is still room for improvement, but
on a Ecovec board with the built-in sh7724 MSIOF0 this driver
gets Mini-sd read speeds of about half a megabyte per second.

Future work include better clock setup and merging of 8-bit
transfers into 32-bit words to reduce interrupt load and
improve throughput.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/spi/sh_msiof.h

@@ -0,0 +1,10 @@
+#ifndef __SPI_SH_MSIOF_H__
+#define __SPI_SH_MSIOF_H__
+
+struct sh_msiof_spi_info {
+	int tx_fifo_override;
+	int rx_fifo_override;
+	u16 num_chipselect;
+};
+
+#endif /* __SPI_SH_MSIOF_H__ */