spi: omap3: add support for more word lengths

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 <[email protected]>
Cc: Jagannadha Sutradharudu Teki <[email protected]>
Cc: Igor Grinberg <[email protected]>
Signed-off-by: Nikita Kiryanov <[email protected]>