spi: omap3: add support for more word lengths

Current implementation only supports 8 bit word lengths, even though
omap3 can handle anything between 4 and 32.

Update the spi interface to support changing the SPI word length,
and implement it in omap3_spi driver to support the full range of
possible word lengths.
This implementation is backwards compatible by defaulting to the old
behavior of 8 bit word lengths.
Also, it required a change to the omap3_spi non static I/O functions,
but since they are not used anywhere else, no collateral changes are required.

Cc: Tom Rini <trini@ti.com>
Cc: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>

include/spi.h

@@ -33,6 +33,8 @@
 /* Header byte that marks the start of the message */
 #define SPI_PREAMBLE_END_BYTE	0xec
 
+#define SPI_DEFAULT_WORDLEN 8
+
 /**
  * struct spi_slave - Representation of a SPI slave
  *
@@ -40,6 +42,7 @@
  *
  * @bus:		ID of the bus that the slave is attached to.
  * @cs:			ID of the chip select connected to the slave.
+ * @wordlen:		Size of SPI word in number of bits
  * @max_write_size:	If non-zero, the maximum number of bytes which can
  *			be written at once, excluding command bytes.
  * @memory_map:		Address of read-only SPI flash access.
@@ -47,6 +50,7 @@
 struct spi_slave {
 	unsigned int bus;
 	unsigned int cs;
+	unsigned int wordlen;
 	unsigned int max_write_size;
 	void *memory_map;
 };
@@ -152,6 +156,18 @@ int spi_claim_bus(struct spi_slave *slave);
  */
 void spi_release_bus(struct spi_slave *slave);
 
+/**
+ * Set the word length for SPI transactions
+ *
+ * Set the word length (number of bits per word) for SPI transactions.
+ *
+ * @slave:	The SPI slave
+ * @wordlen:	The number of bits in a word
+ *
+ * Returns: 0 on success, -1 on failure.
+ */
+int spi_set_wordlen(struct spi_slave *slave, unsigned int wordlen);
+
 /**
  * SPI transfer
  *